I suppose that if you charge your horse with you on top against a wall of (angry) flesh you could mayhem the first few guys in the front but soon you would be surrounded by their angry friends with pointy sticks with your horse badly hurt and afraid while your friend behind you are just pressing his face against your back in a clustefuck accident of flesh, horse and blood... so... how it worked? I can see it working against loosen "formation" where you could, i suppose, hit someone as you pass by and dont get stuck, but how it could have any success against bundled together formations?
You're focusing on the physical mechanics, which is fine, but they don't tell the whole story. You're missing two more factors: one physical, that being that even if you manage to kill a charging horse, that doesn't mean the horse instantly drops; another moral, in that tall men astride big horses are really goddamn scary. More can always be said on the matter, so if anyone would like to make their own writeup on how cavalry work, please don't let this post stop you!
For the meantime, OP, I commend to your attention one of my previous compilations on "How did cavalry work tho", with further input from u/dandan_noodles in that thread.