P.S. I say stun should go with weapon weight. If you disagree please say so.
What you're describing with weight is commonly referred to as 'weapon stun' and is already in place. It happens with every weapon, not just polearms, and is most noticeable when using a one-hander with no shield.
Polearm stun is best described as a stagger, and it is indeed annoying. The obvious solution is to remove it and increase the speed of certain polearms, but I don't think that'll happen until the devs start messing with the hard code or something.
That said, while there are many weapons in this game that cause concern, ultimately, we're standing on a pretty balanced era here, and the hafted blade is fine in my opinion.
The
long hafted blade and similar polearms could use some work, sure, but they're not weapons you should have any trouble with if you're a balanced or agility build.
Essentially, I believe the most annoying issues with them come from playing a character that is gimp'd toward them- such as running around with a one-hander and no shield or playing a heavy strength character, or, if you're feeling exceptionally masochistic, both.
However, these builds are excellent in almost all other situations, and so I think it's a trade-off.