Vision, Hulk, Thor, and even Scarlet Witch could pose a threat to some of the main DC characters.
Unless, of course, you subscribe to the Superman is OP idea and has dimensional breaking powers, in which case, I ask: why the heck would you need a justice league to begin with? So when Superman cowers from Kryptonite he has back-up?
I don't like "OP Superman" (because OP superman is freaking boring and stupid) and as such when I make my predictions I use his classic powers.
Hulk is literally indestructible. The best Superman could do is knock him out. Superman would also have to worry about Thor, who could best his strength.
I doubt he'd get past The Vision, though. You also have to worry about Quicksilver, who could out-run him.