for me there should be simple relation:
knockdown=unballanced, like in 2h
Realistically speaking, something like a warhammer was relatively easy to wield with 1 hand due to it being well-balanced and short. Warhammers wouldn't weigh too much more than a hefty modern household hammer that you use hammer nails and such. If you go and pick up your hammer, you will find that while sure, it is not nearly as wieldy as a sword, you can still easily stop it mid-swing. Let's not forget, that the odds of you being as well-practiced in such things as a dedicated knight are also pretty low. In crpg, the warhammer weighs 3.5kg, or ~5.5. pounds. This seems a little ridiculous to me, considering that the long hafted knobbed mace wieghs 2.8kg, or ~6.2 pounds. The LHKM is just over double the length of the warhammer and has a larger metal head on it. Now, despite the LHKM being wielded with 2 hands (in the polearm grip, not the 2 handed grip) it is labeled as unbalanced. Arguably, with the very small increase in weight, and the fact that you get the extra leverage from the 2nd hand's placement, there is no reason why this weapon would be unbalanced while the 1handed warhammer is balanced.
The only reason why polearm/2handed weapons with knockdown are un balanced are for purely gameplay balancing reasons, I would presume. Being able to feint spam with a much longer, deadlier mace would be pretty OP. Also, the very large weight of the warhammer, and the arguably light weight of the LHKM are also for balancing reasons would be my guess. If the warhammer and LHKM were each given their realistic weights, the warhammer would almost never knockdown, while the LHKM would be much more likely to, given the game's current knockdown formulas.
