2h cav deals less damage (unless you enjoy cav with a 85 length weapon that is) and cannot use shields (or if you use a shield it's 1h wpf anyway). Shields are actually pretty damn important for melee cav so that's a huge drawback. Of course, NA players won't agree here because we all know there's no ranged over there.
Afaik 2H and 1H cav now have the same malus on horseback. Meaning Longsword will do 40c damage, while Arabian Cavalry Sword does 36c damage. I might be wrong here and I've heard conflicting info from devs and balancers about this, but in my testing I found that +3 ACS and +0 lolsword do the same amount of damage with the same build. Also Morningstar seems to do full damage on horse back - that's 41p and will onehit most guys in plate with one hit to the chest.
The non-bastard 2-handers deal less damage. That's utterly retarded imo.
While shield is important, really important, I don't think you should forget the melee ability with the bastard swords either. At least before the nerfs, they were in the top tier of two-handers. You can hardly say the same about any of the 1H cavalry swords.