I agree with your overall sentiment, but there's a difference between intentionally and unintentionally humiliating/hurting someone. Like I said in my last post, both are in the wrong, but the wife is only doing it out of spite and anger, looking for revenge. Which in my opinion, does make her worse, it doesn't make the MC look any better, but it does put Mary in a bad light, when she could have chosen to be the better person. Like I said though, I'm not even playing that path, not my thing.
I want to add, revenge cheating is just as bad, it isn't any better or worse than "regular" cheating. Choosing not to fix the problem and reconcile, and going straight to humiliating and hurting your partner intentionally, is a bad look. If she tried to fix the problem, and he keeps cheating, then that's a different story. She could have went about it better regardless though.