Alien, Sonya, Takeda, Mileena, Johnny.
I'm not even sure I would use the term OP though. The top 5 aren't blatantly obvious, and there are ALOT of viable characters / variations now. Jax is ridiculous. Ermac and Kano are insane. Jacqui has always been severely under rated (sans her t rex limbs), Liu Kang is still Liu Kang, Lao is super good, Erron Black is still a thing, D'Vorah could be thrown into the top 5 discussion, for some reason people stopped complaining about Kung Jin even though he's almost just as retarded as he was in vanilla, a well played reptile is absurd, Quan Chi is still really good, Cassie can fuck right the hell off, Jason and Leatherface have shown viability, Shinnok is still placing in top 8s.
FIVE OP characters is what he wants? If he's gonna get feedback from twitter and there are seriously FIVE characters getting nerfed, then there's gonna be some unwarranted BS coming.