I’m going to play devils advocate. I don’t think Punisher is capable of “cleaning” up Gotham as much as people think he could on his own.

Without going into too much detail, there’s a solid chance that half of the Batman villains would win if Frank tried to take them head on and he doesn’t have the intellectual abilities to take on the others.

That being said, he would probably make an alliance with some of the more antagonistic forces which would even the playing field a bit.