Is it possible to reduce the magnitude of the thrust stun for certain weapons only? I think that a rework of the mechanic that affects all polearms could lead to some unintended balance issues, as polearms are all over the place in terms of efficacy at the moment.
Four-directional polearms like the Long Bardiche, Poleaxe, and Glaive are already on an even footing with the best 2h weapons out there. Making their thrust better would likely lead to problems.
Pikes and Long Spears are the best support weapons in the game and are invaluable in winning the main infantry push during a round. Again, making their thrust better would likely lead to problems.
Two-directional polearms though? I would support a reduction in the magnitude of their thrust stun because, as other people have pointed out, they have very little going for them at the moment. They're difficult to use at a decent level after the turn speed change unless you've dedicated a considerable portion of your cRPG career to two-directional polearms alone, as opposed to the single generation you need to get used to a greatsword if you already know how to melee. They're expensive--everything from the Ranseur on up costs more to use than a Longsword, Heavy Bastard sword, Morningstar, or Barmace. Their thrusts are not appreciably better than those of other polearms when it comes to actual battlefield dynamics--the Poleaxe is better for 1v1 because it has a thrust that is shorter but just as strong and backed up by very good swings to boot, and the length of the Pike and Long Spear makes them better for fighting in groups. The only area in which they have an edge over other polearms is in being able to actually kill horses after you rear them, but the thing is that not even all of them can rear (lol Partisan).
That's why I think that reducing the magnitude of the thrust stun for specifically the Ranseur, Swiss Halberd, Spetum, Awlpike, Corseque, Long Awlpike, Partisan, and English Bill should be considered if the game engine would allow it. It would help to make the aforementioned weapons a better midpoint between the 1v1 power of the four-directionals and the absolute support offered by the pike/long spear, would not require changes to their stats, and would neither completely change how they play nor leave them as the bag of mediocrity they are now.