Whilst I can sympathise with your frustration, I personally have messed up my army composition several times. Especially when trying to move loads of the same types of troops that can only be produced in one province and have been slaughtered when ambushed by the AI with a well balanced army.
You coulkd be being a bit tough on the AI?? - (or I could have mis-read your post and be sounding like an idiot)

Is it is a bit tough to blame the AI for having too many artillery pieces when it was coming to retake a city?

But I do agree that perhaps a "game selection" bar at the start of the game could be a good idea. I am not a fan in any way of the Inquistors or heretics or to be frankly honest merchants (I know that this is additional detail, and detail is what sets these games apart) but if you could tick a box at the start of the game to not have these a part of the experiance it could make many people enjoyment more. It is not that much different to selecting the difficulty setting????