Thats a bit overglorifying the muslims armies, they are pretty fine right now, you must get used to them to get their full potential, mostly use pinning and flanking tactics.

In one of the battles i once only got 4 casualties against a late catholic army(custom battle, steppes terrain).And mongols are pretty good too, although they lack that feircness that made the famous, but they are still fun to play with(custom battle or multiplayer) there are also mongol campaign mods wich are fun.