I'm not enthusiastic for "decadence" -- no one really likes the anti-blobbing mechanisms and eventually P-dox ends up working around them. Government Cap is just the latest incarnation of this and they ended up fixing their fix to the corruption system by letting you spam buildings that take up no building slot.
Ottomans are OP. Again, I detest the Ottomans -- not because they are "bad guys", not because they are OP, but because the AI Ottoman is too consistently OP. What do I mean? I mean I have literally never played a game where the AI Mamelukes beat the Ottomans down. I have very rarely seen an AI Russia, Poland, Spain, Austria or Timurids do anything but contain the Ottomans and while I have not counted to make a scientific study, I believe that I can count on one hand the number of times where I played a "remote" power where the Ottomans weren't the Final Boss of EU4. It's just boring.
Every game I play, no matter what nation I start as, I have to plan to deal with the Otto-blob. Sometimes, I can launch an early decapitation strike (see Hungary, Byz, Austria, Poland, Mamelukes), but the farther away you start the harder it is to break them apart, or alternatively, you need to wait until the end game units fall apart and you've filled out all your ideas, etc.
The manpower, the manpower recovery, the tolerances, the age bonus, the unit pips, the culture group, the religion, the trade setup -- all of that (I think) was designed to make the Ottomans the strongest nation of EU4 and provide a challenge to the player, when the AI was utterly incompetent at things like economic management and it needed unlimited armies to defeat the player. Now that the AI is much improved (believe it or not, it is) alot of these bonuses are overkill.
A supercharged mission tree and new mechanics are likely to make a bad problem worse. Sorry to offend. Just once, I'd like to play a game where the Mamelukes crush the Ottomans or the Timurids become the #1 AI power. But, I'm not holding my breath.