Most of the cavalry issues people are having can be described as player error.
I see dragoons trying to go head to head with lancers and hussars after firing off a single shot. If you want to melee, go hussar or lancer.
I see cavalry charging head on several infantry with fixed bayonets ready to stab. Chances are, you are not going to come out of that in one piece.
I see a small regiment of maybe five players charging twenty plus infantry alone. You're doing a disservice to your team by being so reckless.
I see hordes of cavalry regularly come to a complete stop to try to get the kill on a lone dismounted enemy. Not only do they nearly always TK each other in the process of trying to kill that lone enemy, but they're letting the other enemy cavalry take easy shots at them and their undefended teammates.
A lot of these things just make me shake my head when I see them.
All that said, I don't see how cavalry can possibly be considered overpowered in any sense. My mind boggles how these stealth cavalry people are talking about can pull off these heroic stunts. Nine times out of ten when I charge, even from behind, into an enemy line I'm dead within moments. It's suicide to charge in a line from any direction unaided. There's no amount of weaving or jumping that is going to save you from multiple infantry shooting at you from a close distance.
Of course that's how it should be.
The only real issues I see with cavalry right now are:
1) The horses besides the hussar's light horse are way too slow. All these horses should have their top speed boosted a bit.
2) As others have alluded to, a charging horse hitting a man is going to take him out of the fight if not kill him. For it to do a measly 10% damage, and slowing the horse as well is ridiculous. This is also an easy fix. It should do 30ish% of an infantry's HP, and have less impact on the cavalry's movement. Perhaps also do some damage to the horse itself to compensate for the change.