I don't get why chain or plate would protect you more against the brute blunt force of a charging animal, if anything it should be less, because it offers you less mobility to recover or receive the hit. I feel light armor should allow the player to take less fall damage and less horse bump damage because it would be easier to push yourself off the animal and you would have more agility to maneuver than the current situation. Think about it, would you rather be in a suit of armor in front of a charging horse???
or light enough to maneuver out of the way or absorb the blow with nimbleness since you would be aware that you're about to be struck and offer more ability to break your own fall.
I think it would add more balance to the game.
Again I'm not asking to gimp heavy armor in any way regarding this, even though it would be fair to switch places e.g take the penalty currently given to someone wearing light armor when charged by a horse and give it to heavy armors and vice versa. What I'm asking for is to either even them out or think about it more thoroughly for realism's sake, because the advantages to wearing light armor are there but they are not fully realized.