I don't think there underpowered personally. When I play the demo, at Pavia, and the general and his knights charge as above poster said. They usually do a fair amount of casualties even when my men are braced for the attack.

I still find Calvary highly useful, I don't have them in Agincourt and there's always one or two moments where my archers are quickly struck and my men can't get there as fast as I'd like. In Pavia as others have said the calvary unit (the whooping 40) one of the differences between victory and defeat. Even when my general gets to 8 men he still does amazingly well. This could be though because he usually has 3 gold valor at that stage