LOL that is a nice assumption you're making.One thing I have noticed about power gamers - that are far more interested in boosting damage than boosting defence.
How about making it a feat actually worth taking? Considering how few feats most PCs get (about 3, considering how long the games run) and the competition between ASI and feats, feats are too valuable for something like this--there are better ones out there (both for flavor and mechanics).
And, FYI, MAM and HAM are two of the most popular feats at our tables and are defensive. In fact, we've only had two PCs ever take GWM or SS, both run by the same player, who admittedly is a power-gamer. Most of our players aren't.