i personally think that 2H and polearms are balanced... 2H is usually best when you're standing alone and especially in duels, while polearms are better support weaps and better for spamming in large groups.
The 2Hs have animations that allow them to feint very well, thus confusing the opponent which results in a hit.
Polearms can't do that, wich is why they aren't as good for 1 on 1, but they are very ncie as support weaps because of the range (and stab dmg)
Regarding the stab, i also think that it's balanced (even tough it wouldnt matter if it wasn't, as long as the weapons are balanced overall.)
The polearms (some of them) has better stab dmg, yes... but why is that? it is because of the way polearms are held (both irl and in-game).
Where 2H's are held on the handle, polearms are held with one hand at the end of the weap and the other almost half the way up the weapon. That results in the wielder being able to handle the long weapon better, but it also allows the wielder to thrust harder, thus giving more damage.
The downside of holding a weapon this way, is the short range because you hold almost half the way up the handle - and that is why 2H's actually outrange polearms, which is also why stabbing as close range is easier with polearms.