I had this Al problem when i joined the Nords as mercenary. We fought sa defenders against 1200 units of Swadia in a siege battle.
The Al was so stupid that they totally ignored 4 ladders and constantly come at the same one, and got beat down with approximately 24 units of nords on the upper side of the leaders. I saw this "band" of nords killed around 200+ units, with a few units coming to reinforce them. And at the same time their archers stood in the yard, disregarding the fact that the walls wore completely free.
In this game the Al is so firkin dumb it hurts and spoils the entire game.
I was beginning to wonder is there a mod who enhanced AL behavior?
All the things i sad are in the picture. The "nord wild bunch" , archers down on the left, behind the walls and totally useless, and the attackers coming constantly on one single ladders.
Oh, i forgot to mention the fact that, at the end of the battle the single peasant unit left for the attackers in front of the wall next to leaders, and because non of nords was truing to kill him, i had to retreat the battle although we kill all of them and they kill around 40% of us.