The combat is for the most part fair. Any personal experience to the contrary is probably confirmation bias. You just notice the times when a battle swings against you much more than when you pull off the same rubbish reversal on the AI.
I suggest you mod the marshal section of the job_titles.txt file so that female commanders can be enabled. I know it will go against the cultural norms of Medieval Europe; but this is CK2, not the History Channel. You'll need every 10+ general you can get when you're up against enemy doomstacks. If the price of keeping your throne is either your wife and or daughter(s) potentially being maimed or killed in battle, so be it. You can also remarry and have more children. Don't let traditional gender roles keep you from utilizing good commanders, thus leading to a potential game over. Remember the aim of CK2 is the survival of your dynasty and realm by any means necessary.
Especially when you throw in National bonuses like Prussia's +infinity discipline. If you've got lower discipline than your opponent, then you might need a ridiculously higher number of troops to avoid higher losses than him, even when you win battles.
Combats are really what disapoint me with paradox grand strategy games, and ck2 is the worst.
I think they should improve it, maybe like Endless Space with playing cards (Attack, defense, tactics, charge, long-range...).
I find combats boring and you can't know why you lose or win except with terrain modifications.
Something that bugs me: when two armies clash and fight, there is never a 'stalemate' result, always a victor. The loser then flees to a neighboring province and the victor pretty much always pursues and catches up, over and over thus leading to near or total annihilation of one army.
Wouldn't it be more fun if the armies could sometimes engage, disengage, regain morale and go at it again? Not just the old 'win first fight then reengage the loser into oblivion' every time?
I'd like it if there was a way for both the player and the AI to have a good chance to disengage and not get caught again immediately by the opposing army.
The problem with CK 2 combat is that it has a veery steep learning curve and the real strategic elements dont exsist untill you can get large amount of retinues.
But when your fighting with levies its really just a numbers game.
Pretty much this.