JakeTheBank
Return of the King
It's because of full capacity and what we have seen Superman do on panel. In comics, he doesn't speedblitz people a whole lot of the time, but he has done it. In a forum setting, such a tactic would be plausible, but probable? That's what a lot of people debate. In character, I don't see Superman speedblitzing people or severely exploiting his speed unless he's really pushed to. Planetary strength? Superman's shown that. He may not have busted a planet in the exact same manner that Glads did, but based on his feats and what Superman has done, I find it hard to believe that he's not capable of such a feat. On panel feats are good, great even, but common sense and the ability to connect the dots are important too. We've seen Superman rebuild a city in seconds using speed; would punching someone with similiar speed be impossible for him? Unlikely given his character/personality, but possible? I think so.
Fully confident Gladiator is a myth in the sense that people think he's greatly ampflied beyond normal when virtually every comic he's in that mentions his confidence being a factor is only when said confidence is being diminished. He's fully confident unless it's been shown or stated or alluded that he's not. Otherwise we have to believe (and make up) random confidence levels for Gladiator in stories he's in. And if he doesn't bust a planet or move at FTL speeds during fighting, he must be "less confident"? That's absurd.
Superman holds back a great deal as do many characters in his weight class. I don't see why a bloodlusted/non holding back Superman wouldn't be stronger based on feats and the character's history. Superman doesn't have some conspiracy group trying to make him the king of versus forums.