My STR build is mos def easy mode.
My agi builds are very, very hard. Ath is useless, its called a horse.
Perhaps link WPF to penetration meaning when you thrust a tincan you really punch a whole in them. Also you could add extra multipliers. ie have a heavy curve in the extra out put for wpf, so builds with +150 start to get a massive benefit. That char is more agile and skilled with a blade and is therefore able to hit weak spots in armor more often and harder.
That way your agi builds are squishy but you don't want to get stabbed by a side sword wielding Inigo Montoya, he will take a dump on your day.