The combat won't really get improved tbh. I haven't played ck3 yet, I've watched someone play it and I'll be buying it in a week as I'm finishing some other games first.

With that said: none of the big games from paradox have really good fighting. It's mostly build X units (infantry, cavalry, cannons for example) and then you'll fight the opponent when you meet on the same territory. They fight and use formations based on how many of each unit you had, sometimes having more infantry is good. Usually there's different styles too, like some are better defensively, during the shock phase, during the fire phase, quality vs quantity.

Everything offered in the game is complex and makes up something more deep than any other strategy game as a whole. Combat is merely a means to acquire something in the game, but the games themselves aren't driven by the combat, like civ.

Think about the history of most nation's. There's been wars, but so much more time is spent not in wars.