Polearms used with no shield get -20ish or so length, 2h swords get +50, so a greatsword is longer ranged then a glaive (which is barely long enough if the lancer is stupid and too short if the lancer is not stupid, granted you can evade and slash, and is also the longest polearm you can swing sideways).
Of course, you could use a spear with a shield and outrange them. But then, amazingly, you have no slots for another polearm. So either you pick a polearm which can stop horses and support or you pick a polearm which is great for general fighting, but you can't take both. The argument that all polearms can stop horses, well, ye, but if someone is daft enough to run into a poleaxe stab, then you can halfsword your greatsword if for some reason you want to rear the horse instead of stabbing it in the face.
Check Dezilagels post for my own initial reaction.
But unlike him I like to also inform the guy who failed so hard:
To rear a horse, the weapon itself has to be 140+ length. I am NOT talking about any bonus from animation or hitting the horseman before he hits you; I am talking about the exact reach of the weapon. For a weapon to rear a horse, a lot of stuff has to be correct, one of them being that the weapon length stat is 140 or more. You get it now? No extra reach from animations will help, so halfswording will NOT rear horses, even though it's considered a polearm. It just doesn't have the length.
Here's the criteria list for a "rear horse" to happen:
- the attacker must be unmounted
- the attack must be a thrust
- the attacker's weapon must be of type polearm
- the weapon need to be more than 140 long and deal pierce damage
- the receiving horse must have a forward speed of at least 3 m/s
- the attacker must be in the front of the horse (120ยบ cone starting from the horse's "center")
- the priority of the animation being currently played by the horse must be less than 74 (riding has a priority of 0, jumping has a priority of 2, etc...)