I hope you and others that will come and read this post learn the lesson from now on.
In ANY Total War game, increasing the difficulty of the campaign means more challenge/ betterCAI/BAI,etc., in the way of inteligence. The only thing you get from Hard/Very Hard and Legendary is a bonus on stats and money for the AI. IF and only IF that means to YOU a "challenge" then go on but never ever complaint about any kind of aspect nor the camapign neither the battles cause you have been warned from this day
Furthermore, the mod CAI BAI has been tested and Balanced in the Normal difficulties.
Finally, please don't get me wrong, I'm not trying to be rude, salty or unpolite, just giving you a portion of reality. It is what it is
Hope you keep enjoying this great mod.