This game is called MOUNT and blade for a reason... not dismount and blade
Which is ridiculous, cause why would you want to sit on a horse and stab, when there's an awesome, hard to master fighting system in place for infantry.
The thing is, cav has maneuverability, they will always continue to get the drop on those that are unaware or those already in a fight, without endangering themselves much. Which causes my respect for the scores of cavalry to be really low. If I see a footman get 20/1 I'm amazed at his skill, when a horseman gets that, its no big deal.
The best way too nerf cav, would be giving them more noise, and implement a decent sound engine. But thats not going to happen.
Second best option would be what Thomek suggested. Nerfing maneuverability significantly and buffing horses hp. So they have to think ahead, although giving a little more room for mistakes.