Nothing OP about that, it is like blood god hitting the opponent for a ton of damage.
3png stacks and a bar are required, it really doesn't change much considering you can already get around 65% for no bar in regular MK X
Getting 3 png stacks honestly isn't all that difficult since they became cancelable. And having bar with ruthless is also not hard at all, given that the current bar spending options aren't all that great.
Also, I don't think I know of any combos that get to 65% currently, I think it was 56%? Something like that. Which makes it 15%-20% difference (at a cost of a bar, of course) compared to what
@EGP Wonder_Chef has displayed here. I think it can be assumed that if this goes live, with some optimisations this could get even more damaging.
I haven't really given this much thought quite yet and so I can't say if this indeed is OP or not, but I really think this should be at the very least examined.