I kinda see where you come from, but see:
MechJeb: the name says it all, it's a mechanical version of Jeb. It's supposed to do all kinds of stuff. I, myself, used it for some time just for launches. Some people use all of its features. I don't think any two players will agree what the 'core' of it is
KAC: everything about it is alarms! Again, I don't see how it should lose any functionality; and its UI isn't going to get much simpler by removing different types of alarms
KER: Apart from the DV guide, there's only the flight information windows, right? Do you think KER is bigger and harder to maintain because of them? Those are just reported straight from the game, AFAIK, or most of them anyway. Or is its UI bloated? You can turn the flight information windows off, so the only interaction you'll ever get with it is in the VAB.
I don't see how any of these mods could be simpler, while maintaining their purpose. Sure, a mod that only did DV calculations in the VAB has a niche, but one that also displays the same calculations mid-flight is more useful, at least to me. And the barest MJ ever is already stock, those autopilot buttons. Seriously, launch assist is a thing of the past.