Is KSP in need of a "balance patch" again?

[Corona688]

Cost is probably the one thing squad COULD balance if they really needed to.  Anything else would break everyone's ships.

[klgraham1013]

8 hours ago, Curveball Anders said:

The problem is that there's a lots of opinions on what's fun and balanced.

That's why you never try to please everyone.  Believe in your vision and do the best you can.

8 minutes ago, Corona688 said:

Cost is probably the one thing squad COULD balance if they really needed to.  Anything else would break everyone's ships.

Which is why it all should have been done pre-1.0.

Anyway.  As I said, I'm doing my own balance pass, and the absurdities of cost I keep running into are seriously depressing.  It really makes me question what they were thinking.  Are the numbers literally random?  Did they actually think they contributed to gameplay in some way?  The answers we will never have, and I don't actually expect it to change.  This is what we're stuck with, and it's disappointing, as with so many other things in the game, I'm having to do it myself or rely on unpaid modders.

Edited May 7, 2018 by klgraham1013

[Corona688]

Costs are incredibly easy to change in ModuleManager.

[klgraham1013]

10 minutes ago, Corona688 said:

Costs are incredibly easy to change in ModuleManager.

Again.  Shouldn't be the users job.

[Pthigrivi]

1 hour ago, Corona688 said:

Cost is probably the one thing squad COULD balance if they really needed to.  Anything else would break everyone's ships.

This is an interesting point, because there are so many things that could be improved if we all accepted it was going to tweak some saves a bit. I really do think it would be worth it to bite the bullet on 1.5 if it meant a thorough housecleaning. And its not as if adjusting masses and thrust values would straight up break saves, just some craft currently running on tight margins. And if they made a solid balance/progression pass on the tech tree the new tech tree could just be the default for new saves. 

[KerikBalm]

But they've changed part stats in the past, and that has broke some craft before... so why the sudden aversion now?

Example:

https://wiki.kerbalspaceprogram.com/wiki/Kerbodyne_KR-2L%2B_"Rhino"_Liquid_Fuel_Engine

Quote

1.2

• Specific impulse at sea level decreased from 255 to 205.

I also seem to remember at one point the mass was 6.5 tons... maybe I'm miss-remembering it.

I'm pretty sure that this design, which was already marginal (look at the dV readout) didn't work after the change (it was made before Vectors were a thing)

Spoiler

Balance changes have broke craft in the past. I'm currently avoiding using the skiffs and wolfhounds because I think they clearly need to be re-balanced, and that re-balance could break the craft if its pushing the margins.

As long as saves aren't broken by parts being deleted (like how they kept in the old jumbo 64 tanks), personally I'd be fine with wolfhounds being hit with the nerfbat, costs being changed, and skiffs skippers increasing in mass and thrust, etc....

[Anth]

I checked KSP 1.2.2 compared to 1.4.3 (without the DLC) compared to 1.4.3 + DLC just on the stock plane called the Mallard.

The drag hasnt been changed for the

MK3 Cargo Ramp or the

MK3 Cargo Bay CRG-100 or the

MK3 Cargo Bay CRG-50

Plus I dont remember EJ_SA on twitch ever complaining about these parts having incorrect drag in relation to his Shuttle which he spent so much time on getting to work like the real shuttle, (he actually did something to make his shuttle worse somehow so it would act more like the real one)

If theres no difference between older and newer versions of KSP drag wise. and EJ_SA who has 8000 - 10000 hours in KSP and doesnt seem to have a problem with his most loved craft, I am tempted to think there isnt a problem

He has another 2 simple crafts that use the MK3 parts. one is a space plane that makes it into orbit quite easily and the other is a supersonic cargo plane that he flew around Kerbin.

So...agreed. their drag was designed for Stock KSP with stock Kerbin

[Corona688]

16 hours ago, Pthigrivi said:

This is an interesting point, because there are so many things that could be improved if we all accepted it was going to tweak some saves a bit. I really do think it would be worth it to bite the bullet on 1.5 if it meant a thorough housecleaning. And its not as if adjusting masses and thrust values would straight up break saves, just some craft currently running on tight margins.

They've done it before and the caterwauling could not be believed, some of it even from me.

They outright cancelled another balancing due to feedback.  Nobody wanted their ships broken.

It'll never happen again.

Edited May 8, 2018 by Corona688

[Pthigrivi]

1 hour ago, Corona688 said:

They've done it before and the caterwauling could not be believed, some of it even from me.

They outright cancelled another balancing due to feedback.  Nobody wanted their ships broken.

It'll never happen again.

Well if true that would be unfortunate. KSP is all about designing and refining. Tweaking a few individual vessels seems a small price to pay for a well designed game moving forward. Im also thinking of a lot of other games that have continual balance patches and people just have to kind of roll with it for the sake of quality play.

Edited May 8, 2018 by Pthigrivi

[KerikBalm]

On 5/8/2018 at 10:16 AM, Anth12 said:

I checked KSP 1.2.2 compared to 1.4.3 ... The drag hasnt been changed for the ... MK3 Cargo Ramp or the ... MK3 Cargo Bay CRG-100 ...

Plus I dont remember EJ_SA on twitch ever complaining about these parts having incorrect drag in relation to his Shuttle which he spent so much time on getting to work like the real shuttle, (he actually did something to make his shuttle worse somehow so it would act more like the real one)

If theres no difference between older and newer versions of KSP drag wise. and EJ_SA who has 8000 - 10000 hours in KSP and doesnt seem to have a problem with his most loved craft, I am tempted to think there isnt a problem

Well, I didn't say that the drag has been changed, I've just been using the extended aero information through the alt-f12 window, and its drag is much higher than similar parts.

I'm not saying that the drag is too high that they are unusable, just that its inefficient to use them when drag is a major concern. I didn't know who EJ-SA was, so I looked up his youtube channel,  https://www.youtube.com/channel/UCfG8aSXvP_YhDhGR9jPKZ0w/playlists  and it seems he's using mk3 parts mainly for STS style launches. Drag is much less important for gravity turn profile vs a shallow airbreathing ascent.

Also, I use the parts even in 3x, when I want to make use of a cargobay instead of a payload fairing, particularly for deploying rovers and such.

Spoiler

Here's a mk3 design that makes orbit on 3x kerbin, but minimizing drag when switching to closed cycle is the make-or break part of it:

A different design, less use of mk3 parts, doesn't use nukes, does much better... here after a successful mission

A heavy cargo SSTO on 3x kerbin, making orbit with hundreds of m/s to spare thanks to the use of LV-Ns. Uses only mk2/mk3 parts for fuel storage:

^That design was bearly breaking 10% payload fraction

When I replaced almost all the mk3 tanks with 2.5m tanks, and rotated the mk2 sections, I was able to get a 17% payload fraction... The few tons gained by removing the cockpit does account for a few percent of this... though. Since the payload was on the order of ~160 tons, removing 3.9 tons of cockpit accounts for ~2.5%

Granted I also added more wing area, but all that factors into improving the the L/D causing a ~50% increase in payload fraction, which is huge

I'm not saying that mk3 parts have drag so high that they are unusable. I'm saying that their drag is so high that they are some of the last parts you'd want to use on a spaceplane if you are optimizing it, which doesn't seem right to me.

I've completely phased out mk3 rocket fuel tanks in favor of cylindrical tanks in my designs, and the payload fractions have gone up considerably. At this point I only use mk3 liquid fuel tanks (for supplying LV-Ns with liquid fuel... so mainly a vacuum consideration where drag doesn't matter) and the cargobays. If the gameplay purpose of mk3 parts is for making spaceplanes, their drag properties shouldn't be such that you shouldn't actually use them for spaceplanes.

 

[AVaughan]

Well x3 isn't exactly stock.  So balancing parts for x3 shouldn't be Squads priority even if they did do a balance pass.  As I said earlier the Mk3 parts are shuttle parts, not space plane parts.  Shuttles normally have external boosters and an external tank, and launch straight up, then pitch over into a gravity turn.  That substantially help their max payload fraction to LKO.  

Personally I think that the higher drag is a useful asset for shuttles during re-entry.  If you only want the Mk3 tanks for liquid fuel then maybe just add a mod that enables you to switch some of the 2.5m tanks to liquid fuel. 

[KerikBalm]

11 hours ago, AVaughan said:

Well x3 isn't exactly stock.  So balancing parts for x3 shouldn't be Squads priority even if they did do a balance pass. 

I never claimed x3 is stock. However, x3 works fine with stock parts, its not like RSS where you pretty much also require RO to give you parts with higher Isp and lower dry mass. x3 can help illustrate balance issues because marginal differences have a larger effect in those cases. You could got to Moho and back using nothing but mainsails in stock or x3, and it would be much easier than in x3 for instance. The mainsail's gameplay role is not that of a vacuum propulsion or lander engine, and that would be more obvious in x3.

Quote

As I said earlier the Mk3 parts are shuttle parts, not space plane parts. 

I'm going to have to strongly disagree here. Mk3 parts as we know them now (ie, Porkjet's mk3 parts) came out at the same time as the Goliath and the FAT-455 wings. Lets not forget the cargo ramp itself... while many of the parts are clearly space shuttle inspired, they are definitely not intended as  just shuttle parts. Maybe if they had only come in the MH expansion, and had not come out along with matching "airliner" wings, massive fuel tanks (the real shuttle carried very little fuel for its OMS, none for the main engines), liquid fuel only fuel tanks,  and a cargo ramp, you might have a point... instead, we have stock craft like this Mallard:

They are plane parts. They are meant for making planes, space-planes or otherwise. Vertical launch or Horizontal launch, they are still plane parts.

While the cargobay functions cannot be substituted with another part, if you are concerned about aerodynamic performance, you should use cylindircal tanks in place of the mk3 tanks whenever possible.

[Rune]

On 5/7/2018 at 12:21 PM, GoSlash27 said:

I have no opinion on the Mk2 and Mk3 parts. I've never had drag problems using them. The only time you should be flying a space plane at high AoA is during reentry and landing. Drag is a good thing in that situation.

Check the drag of the short Mk2-Mk1 adapters with the cheat menu. Check the numbers against things like Mk3 fuselages, 1.25 and 2.5m rocket parts, and the shuttle backside (with nodes covered). Then come back and tell me if you don't think that has to be a bug. Its drag is several times what an equivalent rocket fuel tank has! And its the one supposed to be used in planes. Instead, it makes planes based on them need a much higher TWR than planes made out of rocket fuel tanks, and the spaceplane parts, in the end, the worst parts to make spaceplanes.

The long adapters are the same, but less glaringly so, and Mk2 straight fuselages are a tiny bit better, but that only makes them the worst kind of tank in the game, with no aerodynamic savings at all to offset their higher dry mass. Again, in things that are supposed to be used in planes.

 

Rune. And the cost thing? That's just ridiculous.

[KerikBalm]

I should have responded to this post earlier:

On 5/7/2018 at 11:02 AM, blakemw said:

RAPIER is perfectly balanced. It's pretty great as a jet engine, and not terrible as a rocket engine. The ISP is low for in vacuum because you don't need to carry additional weight in rocket engines (or jet engines), all things being equal if you shave off 2t of mass, you can bring 2t more fuel or payload so for missions to LKO it's hard to beat RAPIER spaceplanes.

There are many flaws in what you've said. First you don't shave off 2t of mass. The rapier has a mass of 2t, yes, but only 180 kN of thrust. This is the same as an aerospike, which has a mass of just 1t, so you might say each rapier saves your 1 ton of aerospike mass... but it doesn't even do that, particularly for larger multiengine designs, where you might use a Rhino. A rhino gets ~222 kN per ton, so Rapier closed cycle saves just 0.8 tons of rocket engine... but wait... it doesn't even do that... Both the aerospike and the Rhino have higher vacuum Isp, so now the Rapiers are going to need more mass in rocket fuel... or you could take an even higher TWR engine. These engine mass savings get even worse considering higher TWR booster type engines, or the new Skiff: 1 ton, 300 kN. Closed cycle on Rapiers saves just 0.6 tons of skiff engines... oh and skiffs also have significantly better Isp (although similar arguments apply to vectors and mammoths!)

But its even worse than that because generally you wouldn't need anywhere near 180kN of closed cycle thrust per rapier... indeed some have argued on this very thread that the closed cycle thrust should be halved. Indeed 2 jet, 1 aerospike designs work fine. Also, all liquid fuel only designs are perfectly viable in stock and can get some pretty high payload fractions... so I'd say we can cut this "saving" down by half, every 2 tons of rapier saves you 0.3 tons of skiff engine, for example.  "Ok, well .3/2... Thats still a 15% engine mass saving" one might say, at the cost of 15 Isp (comparing to Skff) or a 20% engine mass saving at the cost of 35 Isp (comparing to Rhinos), which is  5%/11.5% worse... well dV is not linear relative to fuel mass, but its looking pretty marginal already (and I'm not even comparing it to the OP wolfhound with 35% better Isp)...

And... its even worse, because you need the most thrust when switching from airbreathing to closed cycle, and if you use other engines, you can run them while still using airbreathing thrust. You should really look at the difference in closed cycle thrust vs airbreathing thrust when you switch them to closed cycle... which is different for many people's designs, but generally people will switch when their craft starts to decelerate again - which depends on the design of course. Some of my designs I switch when airbreathing thrust falls below 90kn, others (in stock size systems) I take down to lower thrusts... I'm going to say for the purpose of this argument and being conservative that one switches when airbreathers are producing 30kn of thrust. So the switch to closed cycle nets an increase of 150kN per engine... and you really only need half of that anyway, because in stock all rapier designs have plenty of thrust when going closed cycle and 2 jet/1 aerospike designs are just fine for TWR (although in a 3x mod, Rapier closed cycle thrust is pretty important because TWRs are lower due to higher fuel masses, and there is more drag as one climbs and accelerated over 3km/s while still in substantial atmosphere).

In the end given the thrust needed, and that going to closed cycle eliminates your residual airbreathing thrust (whereas an additional LFO engine can fire alongside rapiers in airbreathing mode), every 2 tons of rapiers really only saves you about 0.25 tons of some other engine that is going to have a higher Isp and thus requires less fuel mass.

I'm still convinced that Rapier Isp is too low.

*** Giving them the Isp curve of an atmospheric booster makes no realism of gameplay sense. ***

[GoSlash27]

4 hours ago, Rune said:

Check the drag of the short Mk2-Mk1 adapters with the cheat menu. Check the numbers against things like Mk3 fuselages, 1.25 and 2.5m rocket parts, and the shuttle backside (with nodes covered). Then come back and tell me if you don't think that has to be a bug. Its drag is several times what an equivalent rocket fuel tank has! And its the one supposed to be used in planes. Instead, it makes planes based on them need a much higher TWR than planes made out of rocket fuel tanks, and the spaceplane parts, in the end, the worst parts to make spaceplanes.

Rune,

 I can't comment on the latest patches since Take2 took over. Perhaps there's a new bug. *Shrug*.

Having said that, I've never had trouble making space planes out of Mk2 and Mk3 parts. I've made them with .32 t/w without difficulty, even lower with Mk3. Mk2 and Mk3 have always been draggier because they create lift extremely inefficiently. That's why you don't use them to make lift. Keep them aligned prograde with zero incidence, and they're fine.

Best,
-Slashy

[KerikBalm]

You certainly can use them to make SSTO spaceplanes that make orbit easily in stock, after all, I showed examples of mk3 based SSTOs with a 3x kerbin... that they can be used is not the issue, its a question of that they are worse at their intended purpose than the cylindrical rocket tanks

[GoSlash27]

23 minutes ago, KerikBalm said:

You certainly can use them to make SSTO spaceplanes that make orbit easily in stock, after all, I showed examples of mk3 based SSTOs with a 3x kerbin... that they can be used is not the issue, its a question of that they are worse at their intended purpose than the cylindrical rocket tanks

KerikBalm,
 If they can still be easily used for their intended purpose, then by definition it's not a game balance issue, even if another part makes it even easier.

My $0.02
-Slashy

Edited May 11, 2018 by GoSlash27

[The_Rocketeer]

I strongly support a balance pass.

When it comes to unreasonably buffing parts that don't need buffing, I agree - I don't want any super parts either. Much better to nerf everything into line with the weakest part.

18 minutes ago, GoSlash27 said:

KerikBalm,
 If they can still be easily used for their intended purpose, then by definition it's not a game balance issue, even if another part makes it even easier.

My $0.02
-Slashy

Disagree. Being able to use features for intended purpose does not equal a balanced game.

RTS comparison: Here is a superweapon that will destroy all enemies - it belongs to Team A. Team B has absolutely no counter for it, but that's ok, because its sole intended purpose to destroy Team B.

Edited May 11, 2018 by The_Rocketeer

[GoSlash27]

Well, that certainly is a... confusing analogy

Can space plane parts be used to make a space plane? Yes. Is it difficult? No. End of the issue AFAIC. It would be a different matter if players were driven to using rocket parts to build space planes, but they're not. Therefore not a "game balance" issue.

 The price of guidance fins is a game balance issue. They lead the player to avoid SRBs in favor of gimballed LF&O engines because the latter choice is cheaper.

Best,
-Slashy

Edited May 11, 2018 by GoSlash27

[KerikBalm]

1 hour ago, GoSlash27 said:

Well, that certainly is a... confusing analogy

Well, I'll agree with you here, I don't think its a very good analogy.

I would make a different analogy: suppose you have a first person shooter, and you have two guns. The second gun is more accurate, does more damage per shot, has a higher ROF, and has a larger magazine - it doesn't cost anymore/isn't harder to find. Are these two guns balanced? Is there any gameplay reason to use the inferior gun?

Quote

Can space plane parts be used to make a space plane? Yes. Is it difficult? No. End of the issue AFAIC.

To continue the analogy above... could the inferior gun be used to kill an enemy? Yes. Suppose its not very difficult... then is there any gameplay issue? I would say there still is!

Quote

It would be a different matter if players were driven to using rocket parts to build space planes, but they're not.

Of but they are... driven to but not forced to. The rocket/cylindrical parts are largely superior to the mk3 parts (cheaper per unit fuel, less drag, better mass ratio)... that drives me to use the rocket parts... it seems to drive @Rune to use the rocket parts, I'm sure it drives others, or others would be driven if they realized the drag difference. The parts aren't so bad that they are unusable... but usable doesn't mean balanced.

Quote

The price of guidance fins is a game balance issue. They lead the player to avoid SRBs in favor of gimballed LF&O engines because the latter choice is cheaper.

 Yes, I'll agree, its a gameplay balance issue for 1 out of 3 game modes. Although I'd point out that they don't *force* the player to use gimballed LFO engines, and its not difficult to use SRBs, so I don't see why you have the double standard and don't declare "End of the issue AFAIC."... and we jsut found a pretty good analogy! :p

Also, as an aside, it doesn't lead so much to avoiding SRBs, as using a mix of SRBs and a gimballing engine core. They still work great as side boosters for a gimballing LFO core... the aerospike isn't suitable in that case, but I think its low mass and thrust (its not the TWR I'm taking issue with) also means its not a very good core engine anyway.

I do think some parts are overpriced, but in my experience the overprices parts are still a minority of the cost of a craft, so I never paid much attention...

but yea it is weird that a simple ladder costs 440 funds. It is weird that it along with simple aerodynamic control surfaces cost more than multiple rocket engines (I also think decouplers are a bit expensive). You do have some points, but they apply only to career mode. I think part performance which applies to all game modes is more of a priority - some of these things are minor, but with the OP wolfhound, now seems like as good of a time as any to do a balance pass.

[Pthigrivi]

Yeah I tend to agree with Kerik on this. If a part is designed to be be better as a spaceplane part it should be better as a spaceplane part.

[Rune]

2 hours ago, GoSlash27 said:

It would be a different matter if players were driven to using rocket parts to build space planes, but they're not. Therefore not a "game balance" issue.

But they do. I have retired all mk2 designs, because they underperformed in every metric compared to Mk3, by a large margin, and aesthetics alone wasn't enough to offset a 10-20% payload penalty, and a longer climb to orbit. Now, it's not something that is easy to find out (insert comment about bugged aerodynamic indicators showing arrow proportional to node size, not drag amount), but when you start getting down to the nitty-gritty details, keeping track of ratios among your SSTO fleet, it quickly stands out: Mk2 designs underperform in a consistent matter, due to excessive drag. Mk3 vs rocket parts, yeah, the rocket parts win hands down, but it's less obvious, and you could mention the improved thermal tolerance. But Mk2 vs Mk3? Makes no sense, game-balance wise.

 

Rune. They are even quite up there in the tech tree!

Edited May 11, 2018 by Rune

[blakemw]

7 hours ago, KerikBalm said:

There are many flaws in what you've said. First you don't shave off 2t of mass.

Well I was coming from the angle of it being a 2t jet engine (compared with 1.8t for Whiplash), the RAPIER and Whiplash when treated as pure jet engines are fairly comparable, the Whiplash is a tiny bit (almost but not quite unmeasurably) better at pushing planes through the sound barrier and uses a little less fuel, the RAPIER gets an extra ~150m/s top speed so the plane needs less LF/Ox for orbital insertion. Putting aside the cost, my preference for spaceplanes is the RAPIER even as a pure jet engine i.e. for Jet + LV-N, or even Jet + Aerospike.

Given that a Spaceplane needs jet engines and the RAPIER is equivalent to a Whiplash you're essentially getting a rocket engine for free in terms of mass - or maybe 0.3t, but you don't even have to use the rocket mode for it to be a good jet engine. And if you're only going to LKO (which kind of makes sense with spaceplanes, not much point dragging an entire plane through the void) then you only need ~800m/s out of rocket engine and low ISP is really not a problem to LKO, high ISP only truly becomes a large benefit when going much further in terms of deltaV and when the rocket equation really gets brutal. But of course it's common to add a LV-N for this circumstance, the RAPIERs can still provide high TWR for lifting off from high-gee worlds (which whiplashes can't) while the LV-N provides long range.

It can be argued that the RAPIER in rocket mode has more thrust than it needs (about twice as much in the way players often use RAPIERs) this means spaceplanes can work well with a 50/50 ratio of RAPIERs to Whiplashes, though that is only a cost-saving measure and it's only because of poor use of RAPIERs, when using them to the limits of their jet mode (i.e. a SPH TWR of 0.3) all the rocket mode thrust is useful.

Even taking into consideration cost RAPIERs are a remarkably economic engine if you push them to their limits. A 2x RAPIER spaceplane can deliver about the same amount of payload as a Mainsail SSTO and at about the same upfront cost (there is huge scope for scrooginess when building planes...). In fact, if it weren't for the fact that spaceplanes are an order of magnitude harder to build than rockets, I'd say the RAPIER is actually overpowered rather than perfectly balanced, but since most players are using only a fraction of their capabilities it's probably fair.

[blakemw]

5 minutes ago, Rune said:

But they do. I have retired all mk2 designs, because they underperformed in every metric compared to Mk3, by a large margin, and aesthetics alone wasn't enough to offset a 10-20% payload penalty, and a longer climb to orbit. Now, it's not something that is easy to find out (insert comment about bugged aerodynamic indicators showing arrow proportional to node size, not drag amount), but when you start getting down to the nitty-gritty details, keeping track of ratios among your SSTO fleet, it quickly stands out: Mk2 designs underperform in a consistent matter, due to excessive drag. Mk3 vs rocket parts, yeah, the rocket parts win hands down, but it's less obvious, and you could mention the improved thermal tolerance. But Mk2 vs Mk3? Makes no sense, game-balance wise.

 

I'm in the same camp, though I still use Mk2 parts for the utility (i.e. cargo bays), just never for dedicated fuel storage.

 

I've found in testing that a single RAPIER can push about 20t of Mk2 plane through the sound barrier (in level flight across the ocean). Or about 30t of 1.25m/Mk1 plane. The payload penalty for Mk2 is very large, it can be reduced a bit by adding more wings allowing a better angle of attack (which really makes the lifting body aspect of mk2 a joke), but much of that added plane mass is wings, 1.25m/mk1 planes can go really light on wings. Mk3 parts perform more-or-less identically to mk1 parts, maybe a little worse. 1 RAPIER can push about 35t of 2.5m plane through the sound barrier, it is definitely more than mk1/mk3, but more of a 10-15% increase than the ~50% increase from going from Mk2 down to Mk1/Mk3.

I find that Mk3 is usually worth it for the benefits they bring: improved impact and thermal tolerance, what seems to be better structural strength (could just be due to lower density, opposite to how Large Holding Tanks love to come apart at the joints), large flat surfaces for convenience of surface attachment and utility parts like LF fuselage, passenger cabins and cargo bays.

When comparing with Mk2: smaller planes don't tend to have thermal or structural problems (it's the old square-cube law at work) and the Mk2 parts are a simply awful shape to work with, which leaves utility as the only reason to use them.

[KerikBalm]

10 hours ago, blakemw said:

you don't even have to use the rocket mode for it to be a good jet engine. And if you're only going to LKO (which kind of makes sense with spaceplanes, not much point dragging an entire plane through the void) ...  my preference for spaceplanes is the RAPIER even as a pure jet engine i.e. for Jet + LV-N, or even Jet + Aerospike

...

It can be argued that the RAPIER in rocket mode has more thrust than it needs (about twice as much in the way players often use RAPIERs) ...

Even taking into consideration cost RAPIERs are a remarkably economic engine if you push them to their limits. 

I agree with most of this. Rapiers are great engines for SSTOs, their jet properties alone are enough reason to use them. I'm just saying that their closed cycle is a bit rubbish. In particular with the wolfhound. If you're looking at other engines (ie wolfhound, LV-Ns, aerospikes) and using the rapier as a pure jet, then I think that says something about the closed cycle mode (ie, its not very good).

Again, I'm asking someone to explain why it should have the Isp curve of a booster engine. Its got better atmospheric Isp than a LV-T30, but worse vacuum Isp... why?!

What is the gameplay purpose of giving them a good Isp at 1 atm, but a bad Isp in a vacuum? this makes no sense given how they are used, and doesn't match with the real world analogue (well... real-ish world, the complete engine hasn't been built yet, but subsystems of it have been built)