Gladiator's only chance is ranged attacks. If he tries to melee he'd get beat down.
That said, ranged attacks shouldn't be tough to pull off. CS has no speed or jumping feats to close the gap, though it wouldn't be a stretch to assume that he could cross large distances by jumping.
The only question remaining is whether Gladiator could actually hurt Steel from a range. Steel really hasn't been hurt by much of anything.
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"And then there was nothing. A once broken something now void.
And on the first day, Doom spoke... 'Be.'
And then there was life."
Thunderclaps to his ears will probably do more harm than heat vision unless someone has scans to the contrary. Guy doesn't even flinch while bathed in molten metal.
Personally, I've always been one for relative showings over cheese feats. Citizen Steel should on paper be much weaker then Gladiator but in the JSA he came off at least as strong as Superman imho. Now while I think Superman was an ineffective weak feeb in that setting, that's just my opinion and doesn't change what was portrayed in print.
So Citizen Steel for the win in a slug fest I guess. I have no doubt however, that if the tables were reversed, we'd here a lot about how weak Gladiator is for not being able to do this or that.