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.
And while you may have never heard of him before now, you can still see the Diomedes archetype pop up again and again in pop culture: Legolas in The Lord of the Rings, Snake Eyes in G.I. Joe, Leonardo in Teenage Mutant Ninja Turtles, and especially Superman in the DC universe. They are the people (and turtle) who are reliable, morally uncomplicated, and generally superior to all the other characters. While we love them, we will never be willing to watch an entire movie about only them.
Those heroes are pillars of solidarity, they are ideals, but unfortunately they have nowhere left to go. For an audience, at least an adult audience, we want the central character to change for the better by the end of a film. We want someone who is deeply broken, who is struggling to keep himself together in the face of adversity, and most importantly, we want a character who isn't invincible. We love Spider-Man and Batman because they are driven by complicated, selfish emotions like guilt and revenge to do extraordinary things under the constant looming threat of death. Superman is what each of those characters would look like divorced of any such threat or ugly motivation. Is it still heroism to leap into a burning building when you know it can't hurt you?
That's why making a movie that's only about Superman represents a fundamental misunderstanding of why we love superhero movies in the first place: We aren't nearly as interested in acts of heroism as we are in the madness it takes for vulnerable people to become heroes. The only way to fit Superman into that mold is to strip away some of his power, but the problem with that is ...