lol @ classic Thor fanatic move ... "pretty sure X was/were holding back" ... yes, when Emma Frost amped by the PF is scared of Rulk and trying to kill him (because she fears he'll smash her), she's holding back.
What it really is, is simple. Thor can be kicked around and beaten up by many characters, those same characters cannot do that to Rulk. It's not possible for them to dominate him, physically, so they attempt other avenues of attack or bfr.
It's not "holding back", it's being ****ing smart.
Look at how powerful Phoeclops' OB was, it knocked Rulk through Utopia, by comparison Phoeclops went very easy on Thor.
Also, Gladiator got gang-banged by the P5, it's natural that he would be much worse off than Thor, who just gets beaten up by individual avatars.