If you had to read The Iliad in school, then you likely remember that it's almost entirely about Achilles being really, really angry and killing a bunch of guys. The son of a goddess and destined for glory, Homer won't shut up about how Achilles has no equal. Achilles is, in all respects, a superhero before superheroes existed. But unless you're the type of person who squandered your college years in a Classics Club, you probably don't remember that there's one other Greek warrior who consistently and quietly proves throughout the entire epic poem to be just as great if not greater than Achilles. His name is Diomedes, and understanding why he's so forgettable is crucial to understanding why Superman can never be the center of his own story.
Diomedes is essentially Achilles without the existential crisis. He is younger, smarter, and more consistent. He defeats everyone he faces, and when he runs out of Trojans to kill, he starts fighting and injuring gods instead. Not even Achilles can make that claim. The Trojans, cowering in their walls say, "He fights with fury and fills men's souls with panic. I hold him mightiest of them all; we did not fear even their great champion Achilles, son of a goddess though he be, as we do this man: His rage is beyond all bounds."
That's him stabbing Aeneas, father of Rome, right in the bazooka. For some reason the Greeks put all their best action comics on the sides of jugs.