I think Frenzy was the best example of a villain turned hero, but not utilized in the best way. She was a Magneto fanatic, turned X-Man, even if begrudgingly. The effect of AoX probably hit her harder than anyone else, save Rogue (via retcon). She got a taste of being a hero, a "good guy" and didnt want to do it just because of her manufactured feelings for Cyclops, but because of how it made her feel. She effectively erased old self, down to her appearance and embraced a new life as a X-Man. She should have gotten more attention in Legacy and its a shame she's little more than a plot device in Inhumans. IMO she shouldn't even be there. But the current climate of X-Men doesnt really bode well for her type of character anyway.