Horses have too much HP & running into a chambered weapon should hurt the horse (but, if you want to argue realism, so should the horse corpse, both to the rider and especially the trampled, so stabbing a horse upfront with a short weapon is a risky proposition).
However.
A running light-armoured archer has no right complaining about how he gets trampled wearing his rags; don't care if the kill gets added to the cavalryman or the Champion Courser gets the kill, but an agile character could always, pre-horsebump, avoid damage by intentionally jumping into the horse. Which is quite easy, since there's no inertia for infantry in warband. It was the stupidest defense in the game.
If you want to see less horses or getting kills as a horseman be harder, nerf horse survivability which has been practically doubled since the early days of crpg.