Oh that's actually a very interesting take.
I'm biased because I've recently read Tokyo Revengers which is about, among other things, how a good guy can snap definitely over a tragedy happening to them.
So with that knowledge I can say: we are very lucky to have an actual hero in Ash, because many times he could have lost all his morals and hopes and be, indeed, simply mad. He would probably build an empire with NY gangs to rival the Corsican mafia or even the Chinese. He would keep his bright brain because as mad as he is he wouldn't waste what he earned and actually saved him all these years.
Villain Ash would be cruel and fierce, giving no emotion with whoever he is, very intimidating because of how cold he looks like. Also, his eyes. He'd look at his men or collaborators like if he was planning a hundred different plans to take them down without being noticed.
Also what villain!Ash is, is what our Ash feared during the discussion between him and Eiji "I don't feel anything even after killing someone". I think that once he'd pass that, he would be unstoppable. That's why he would need to totally lose his morals if he wants to play that role of a villain.
BUT ON THE OTHER HAND if he was just a mad dog, then it'd be the most fearful serial killer of America, for sure. I think that in this case he would aim at sexual predators mostly. But with time, he wouldn't make a difference between his targets which would make him VERY dangerous, more than before.
But I have to say as much as it kills me to think about it, the "he'd lose literally any hope" is the trope I would enjoy the most if we talk about angst-level.
But god I hate any of them HAHA but thank you anon I missed making angsty hcs about BF.
Also sorry if I misunderstood I read "villain Ash" suddenly my brain worked by itself.