Even if you give guys more wpf from agility, a lot is just going to get wasted on armor reduction, and they won't notice any difference except for the few that choose to dress below the armor cap. More wpf from agility also weakens WM, since you'll have enough with 0WM and will sacrifice it for more athletics and agility.
I think wpf reduction from armor should be a linear reduction instead of a %-based reduction. Even in light-medium armor, the wpf reduction of a guy with 160 wpf is more than a 111 wpf strength build in plate, which is pretty ridiculous. This solution is build-neutral, does not increase the wpf cap, and is easy to implement (no respecs required) if one can alter such data.
An extra WM point gives ~9 extra wpf. If 3-4 extra points are getting lost each time due to % based reduction, that just dilutes the skill, especially when the differences in wpf is not that great if you are melee in one weapon type. -30 on an agi build would be -30 to a strength build with the same armor.