mmy still has 150 base attack.
252+ Atk Huge Power Mewtwo-Mega-Y Searing Sunraze Smash vs. 252 HP / 252+ Def Audino-Mega: 650-766 (158.5 - 186.8%) -- guaranteed OHKO
any physical walls like slowbro, doublade etc js get nuked by mmy's special moves.
HP mmy is really just really big role compression