Another issue is that the AI seems to waste a bunch of resources in nonsensical MAA picks.
While a player decides "I think I'll go for some Heavy Infantry now" and picks bonuses to HI, then picks an accolade to boost them all further, the AI is building nonsense like Light Infantry mixed with Heavy cav and archers.
Personally, I'd like to see the AI dynamically watching the enemy armies it plans to go to war with, delete some MAA, rebuild certain holdings, reform their MAA to counter what they expect the enemy to use and then declare war.
But i'd settle to just having each AI have their own specialty and, at least, making good use of them.
I think there is a bigger underlying issue. When the player starts a game, he will probably look at his income and see that it's around a measly + 3 gold or so. So what most people probably do is to first invest into economical buildings to be able to invest into military buildings later.
The player will probably also try to keep the castles and duchies he has build up over the generations. The AI does neither of those things and so it will sit at the + 3 gold income for the biggest part of the game. The AI just has no plans, no goals, no sense at all. While the player will be rich after a few generations, most AI rulers will go bankrupt just by raising their armies.
This is a common strategy in all strategy games, specially RTS.
Of course, if we were playing Starcraft no start would be better than simply building nothing but workers, workers, and more workers until you build bases and more workers to mine all the resources from the entire map and only then start investing in military units and start spamming them as if you had infinite resources, completely overwhelming any opponent.
The reason why we can't do that is because there's an opponent on the other side, so if you build nothing but economy your enemy will zergrush and burn down your bases before you can do anything.
The same needs to happen in CK3, players are building nothing but economy at the start because there is no threat stopping them from doing it, if the AI was VERY good at creating military buildings early, and mercyless towards weaker neighbors (including your fellow vassals) we'd be having a very different early game experience.
Try playing Nobunaga's Ambition: Awakening and you'll see what I mean, the AI in that game is ruthless, specially on the higher difficulty, if you raise your armies to attack one side your neighbor, seeing your empty castles will 100% raise their armies to attack you, their AI will also always try to make alliances with their other direct neighbors to avoid getting attacked when they move against you too, so if you don't build up armies, along with your economy, you'll be destroyed, if you don't make alliances too you'll eventually get surrounded by many alliances and nobody will have your back, in that game you don't build armies early or send gifts to build up relations with neighbors because you want to, you do it because you need to.
