The BAI is getting there though. I recommend you keep watch, I'm having very difficult battles in my games. Open field and unwalled settlements only though, walled settlements AI still often bugged.
Now if I dont have as much quantity/quality than my AI enemy, I can only guarantee a valiant defeat at best, if I dont have a brilliant tactic up my sleeve.
The CAI is still doing random things sometimes, but its getting there too. The worst CAI problem atm is the "transport navies" constant cruising problem, and the locked diplomacy relationship perma-wars.