I wish CK3 was harder on these points:
AI towards player: More opportunistic, more aware of player being busy fighting a big war (but not so that 10 realms jump on you xD), better at building armies and having larger levies, and better at their economy and vassal management.
Traits and AI behaviour:
Traits are more importsnt to the player to role play and harder to cheese, or ignore to play the most optimal way. If you are a sadist, then make me a sadist. If I am honest make me more honest. Also I never had a sadist son or cruel either, I lile that i can be a good father bt sometimes other things in life make you kid something else like trauma.
AI should be much more rpg oriented and if you have a scheming vassal then scheme, if you have honest and kind vassal then dont scheme and murder, unless its against a tyrant or something.
Opinions and advantages: Could be a little more dramatic, having a larger impact.
External Internal & ReligiousThreat: It should be a triangle dance, keep your realm stable among your vassals, keep your enemies abroad at bay and keep your people to the one tru faith.
Lost a battle, ok vassals might have slight dislike of the situation. Lose a war or two, well maybe god is punishing us because of our sins? Well we need a new direction (heretics rise up and some vassals seek answers there), btw are you fighting a civil war? Weakness, your neighbors will raid your lands and leave you even weaker... whispers of invasions are being reported. What? Weak? I AM NOT WEAK, well now your vassals believe that too so watch out for factions and schemes.
The triangle dance, the dance a count can do blindfolded but an Emperor might stumble and fall.
"cheesy ending but it works"