This could be a solution to the strength stacking that people do nowadays.
You can get a decent amount of wpf without any weaponmaster!
If the free amount of wpf you get per level get's nerfed, and rather shifted on to weaponmaster, the AGI vs STR choice would be much tougher.
Mind you that such a suggestion should not allow extreme amounts of wpf to be hoarded in wpf builds. STR builds without weaponmaster or very little, should still be viable, but a bit nerfed compared to what it is now.