Definitely not removing it! Making certain enemies during particular quests be less resistant to damage is more along the lines of what I was thinking.
MoL
To me, the single most annoying thing about MC is the enemies running willy nilly all over the place, instead of engaging in more realistic mounted melee. Historically, mounted combat was not running full speed all over the landscape taking wild swings at each other as you passed by. Once engaged, mounted combatants often remained in close quarter melee.
The lesser annoyances would be the speed up/slow down mechanic and that sometimes the mounts feel more like boats on water than horses on the ground (even considering speed an inertia).