If I was an making Ultimate DC Universe…well, I’d probably need to do a lot of research into Regular DC first. But one crucial difference between Spider-Man and Superman is—and bear with me for a moment—power level.
Spider-Man is generally framed as an underdog. Sure, he can stop trains bare-handed and jump up skyscrapers and bench-press a jumbo jet, but he consistently fights supervillains who are even stronger than that, or who have powers that hard-counter his spider-powers. He can’t just punch his way out of problems; he almost always has to use his head, find some weakness or clever trick.
Superman isn’t averse to using weaknesses or clever tricks, but quite often, he doesn’t have to. He’s generally treated as the most powerful guy on Earth. Most of his famous supervillains are either physically weak masterminds like Lex Luthor (whose schemes can’t be countered by Superman’s powers, until he puts on a robot suit) or apocalyptic monsters. Doomsday is strong enough that Superman doesn’t need to hold back against him, and that parity is terrifying enough that people call him Doomsday.
Peter Parker in Marvel’s Ultimate Universe is a little guy who can choose to be a cog in the system, or fight it and get crushed. When he takes a bullet to protect someone, he bleeds.
But Clark Kent isn’t an everyman superhero; he’s the superhero. The archetype, the paragon, the gold standard. When he takes a bullet, he has to make sure it doesn’t ricochet into a civilian. He can’t fight the good fight until “his lifestyle catches up with him”; he’s faster than a speeding bullet, the lifestyle isn’t.
Which isn’t to say he’s omnipotent. If Lex Luthor never puts on a robot suit, Superman’s powers can’t counter any of his schemes. In the socioeconomic or political arena, Superman is at best a celebrity. He can punch tanks, but if Lex Luthor gets elected president and makes himself a dictator, Superman is less capable than Tom Cruise. What’s he going to do? Punch cops and soldiers until they let him be dictator?
If Ultimate Spider-Man is a story about an earnest superhero who can’t survive in a politically-cynical world, Ultimate Superman should be a story about an earnest superhero who can survive a politically-cynical world, but can’t change it. Or at least who struggles to change it, despite his immense strength.