First time I have to disagree with you san.
You know that 1.3 weight almost never gives you a knockdown? A Winged Mace with 1.7 weight (unloomed) already stuns very rarely. Your proposal would make the weapon completly useless. Not even talking about removing knockdown from one handed blunt weapons. I am sorry, but that's just ridiculous.
There is almost no weapon that gets stunned by the Spathovaklion. Only one handed weapons which are used without a shield and which have less than 1.3 weight are affected by this. I guess this is quite neglectable since the weight of most mid/high tier one handed weapons was increased to 1.4+.
There is a good reason why Spathovaklion is
slightly better (well, it always depends on your build) than most other one handed blunt weapons: it is much more expensive (nearly twice as much upkeep as the Winged Mace for example, which has -5 lenght, -0.3 weight, -1 speed and the same damage). It would also be unrealistic to reduce the weight compared to other maces since Spathovaklion is almost completly made out of metal.
Internal one handed blunt balance is fine. No reason to fuck around with it.
12% stun chance isn't that high if you take into account that you still need 5+ hits to kill an enemy with high strength and armour. Your enemy can also use the barrel roll to avoid getting hit again.
I usually always enjoy your ideas, but you are completly wrong this time.