1) all the 4D polearms should be unbalanced
2) and pretty slow
3) but each hit should be a shock hit.
4) they should stun for an X amount of time
All 'let's take all X and make them Y' are bad ideas, except nerfing archery of course
I converted your preposition to 4 points and will say this:
1) Error, people learned to fight with polearms and weapon masters produced balanced good polearms, even for nobles.
I will take the poleaxe argument as my defence. Turning all the polearms to unbalanced will destroy the beauty of differences between polearms and styles of polearm users and the truth of class specification, I mean: hoplites like it with shield and pierce, knights use expensive balanced fast poleaxes and vikings use terrible deadly great stunning axes.
2) Speed reduction may be a good contra for using a powerful weapon (as it is for the great maul), but powerful axes are already do too much damage, so we can just slow great/long axes down, except poleaxes (which are supposed to be fast and balanced and dealing a lot of damage, they should be more expensive, though, like 20k. Or we can take away their stun effect but make them cheaper or crushthrough(!!!) in the secondary mode), and make them unbalanced.
3) We have already polearm stun which is deadly in battle due to 3vs1, if a player survives just the first hit, which is not always happen.
4) see 3)
I see a buff request behind this, and the one which will bring damage to the variety of arms and styles.