Heres some suggestions about fixing cav. Just some ideas.
#1 Fix heavy cav armor. it took 13 swings overheads to kill a champion plated charger with no rider with a 6 PS and a 43 damage 2 hander. I'd recommend a 33% nerf on cav armor across the board.
#2 maybe slow cav down more after bumping someone. I think this was done before but along with slowing acceleration it nerfed cav too much. Maybe just add back the slowing a horse down 50% would work.
#3 Maybe add fall damage when dehorsing someone. In real life you think flying off a horse at full gallop in heavy armor isn't going to hurt?