Dont forget that the AI behavior is hard to "control"...
The cav is particularly bad to play because they have a hard time couching and if they are still mounted, against infantry, they will try to thrust lances without speed, in close quarters combat...
Best tactic for cavalry is to make them follow you, and you pass behind the enemy squad you want to attack: making the cavalry effectively bump the enemy.
When you have sufficiently "surrounded them" with bots, press charge, wait a few sec, and tell them to follow you again and do a bump charge again, or make them dismount and fight (because they are way better at foot most of the time).
Personally I just control them with move orders, it keeps them in formation. After each charge, once they start to split up or generally faff about too much, I regroup them with a move order, get them to where I want them to be, then order them to charge again. With cavalry this generally needs to be done more frequently.