I'm not trying to make conquest more of a grind but make it more realistic and force the player to become more involved in the game so that every decision is important and every decision involves trade-offs. Every step should involve a decision or activity or event.
The purpose is to make the game more immersive.
It does already. But those are all related to increasing one's own power while diminishing that of the others. I'd love a more in-depth and immersive game, but EU4's mechanics simply don't handle it well. You're talking about autonomy and corruption, but what do you do once you've reached your breaking point? Game over? Simply put, once you've expanded to a degree that makes any more territory impossible to incorporate effectively or takes large amounts of time, you just end up in a situation where you can't do anything compelling anymore, except beat up people for money or such.