I agree. It's pretty silly that you can't really slow play after you took the route of being a vassal. The AI targets the player faction all the time, especially since being chosen the ruler, you'll be fighting all of the factions pretty much all of the time.
In my current playthrough I really tried to play it slow and enjoy all the fief stuff they added, doing the quests and seeing how the prosperity works and all that. But it was just impossible as if I wasn't present at the warzones, the AI just couldn't handle 3-5 wars at the same time.
So I had to start eliminating factions and we're currently down to Battania with 5 towns and Vlandia with about 10 towns and I control the rest. I have 3-4 times the strenght of either of them and I can really cave their faces in when ever I wish. Still, they rather declare wars on me like just a few weeks after the previous. They demand outrageous sums for a peace (which would probably just last for a few weeks anyway) even though they really don't have the muscle to do so.
And this isn't really a problem. Sure, I can conquer all of Calradia, but it's reeeeeallly booooooring to just gather up 2k troops and chain siege everything with the same exact tactic.
So, more peace time content AND MORE ACTUAL PEACE TIME, please.