On the ground Superman has many options, full screen he's either gonna laser the ground or do that standard projectile game. React accordingly, yes, you do have time to see which laser it is. You can also EX swamp hands if he starts getting predictable with it, but watch out for his meter, cause that thing hurts, 95% sure you can dash after both blocked, so whatever. Mid range he's going to super man punch, f+2,1, and all that shit. Keep on your toes and out poke his ass. f+1 and 2 are your best friends in a poking war.
In the air, he can dive kick, or air laser, if he air lasers, you can jump forward, or dash once before it gets to you. After you block it, you can dash one more time. If he does air laser mid range, you can dash and d+2 him. If he dive kicks, pretty sure you can punish with 2.
if you're getting closer to him, keep him out the air, that's the thing that gives Grundy the most trouble, out poke him and keep that life lead point blank, I've lost several times trying to run away with a life lead and not being able to react to the proper laser.