The same could be said of Superman's physical prowess. I mean, dude has dragged the earth around, been smushed by planets, been caught in a supernova, is almost as fast as the Flash, and can get even stronger from the sun. J'onn and his telepathy would do a halfway decent job, but he'd have to take down Superman in the physical sense and J'onn is simply not that strong. As for intangiblity, yeah, Superman probably couldn't punch him well, but he has to unfaze at some point and Superman would just stomp him before he could react.