I might need to restrain a bit the over agressivness of AI that just tend to inicte player to do as well. A few way to explore : peace of god at game start to let the holdings specialize a bit ; limitation on DJ CB that are just too much automatic, easy and so boring. Maybe also a crown law to set a long term policy to be warry or more peacefull (or defensive vs offensive) for one full reign. I've tested the latter to specialize republics into pure merchant rep. (more money, less troops, less CB) a more state-like republics (less money, more troops, full CB).
I wouldn't mind some kind of "peace of God" modifier to give time for the lands to build up. Setting up the AI to only be defensive would be interesting.