I too play career, and agree with a lot of what's being said. I see career mode like this:
KSP is a private space program, companies employ us to fulfil their orbital tasks. KSP could be a public space program, funds could be delivered via a "3 month budget" type system that increases as we achieve things, like a crewed Mun landing or Duna drone capture, or it could be somewhat proportional to science rewards (as exploration is about learning things after all).
This means you could properly throttle income, and it does allow disadvantage for just time warping to the next budget, because that might mean you miss a transfer window anyway, but it also means you're not left with an unplayable career because you accidentally "dissambled" all of your early rockets.
It could have a hard cap as well, which would leave you with a nudge to go build off world, use ISRU to build rockets yourself rather than buying them because the money isn't just lying around by the millions for your interstellar drive.
I don't think there's anything inherently wrong with funds, it just takes the right approach to feel satisfactory for the player and not be an arbitrary hurdle, which is a fine line sometimes.