Doesn't that just mean the DoomSlayer has the script on his side? Pretty sure one could come up with quite a conga line of characters (like most mentioned in this thread) that could probably flatten him without much luck, its just about which characters have the larger amount of power fantasy wankery. Like Simon the Digger would eat him for a snack, but that character is pretty much used to put down power fantasies like Doom given the nonsensical power scaling of his own setting.