Going by some showings it can sure be said that Superman is more versatile. In terms of raw power, Gladiator however should far outpace him. IIRC he has destroyed a planet, smashed Wonder Man into the core of a planet, etc. At his classic levels Gladiator was certainly "pre-Crisis" or in that sort of area. And I believe he once did pretty well against Ego and SS, I don't think Superman would stand a chance against either of those two at all. In a fight Gladiator would win, in a circumstance that requires something other than combat (like the aforementioned things with lightning storms, black holes, etc) Superman would win.