The early cavalry lancers were using light lances propelled by the strength of the arm. You can see on the tapisserie de Bayeux that knights were using their lances with the arm ready to strike.
Later on in the Middle Ages, with the discovery (or rather importation) of stirrups (the straps attached to the saddle in which a rider positions his feet to have a strong stance), the art of lancing evolved and knights could use their lance blocked against the body, firmly bent on the horse's back to use the strength and speed of the horse to increase the power of the lance attack (what we call couching the lance).
In c-RPG, when a rider uses a polearm attack (LMB attack) from the horse's back, he gets a damage bonus from the speed of the horse (and from the power strike skill, afaik). This results in very powerful attack, with 99% change of killing targets in one hit. Couching the lance is not really used as it is much more difficult to pass and the extra bonus to damage is just not necessary.
However, using the speed of the horse to boost a polearm attack could not (and did not) work IRL because of a simple physics rule. The power that the lance conveys to the target is reciprocally conveyed to the arm holding it. In simple words: a cavalryman holding his lance in one hand could not sustain a hit on an (armored) target without breaking his wrist or, in the better case, losing the grip.
So much for the historical and physical justifications. Here is my suggestion:
- Polearm attack from horse's back should get the damage bonus from powerstrike only. This attack propelled by the rider arm's strength is fast and swift, similar to an infantry attack but from a higher position.
- Couching the lance should get the damage bonus of the horse speed only. Couching the lance is an advanced technique, more difficult to place (no spinning lolstab) but would be the supreme attack guarantying a kill in one hit.
This would prevent cavalry from piling up one-hit-kills with simple polearms attack and would make the couching attacks (and the great lance) worthwhile as they should have always been.
Feel free to contribute but please keep it constructive.
EDIT: added a poll