Nah commercial success definitely corresponds to relatability. There's a lot of stuff I don't like and think is garbage but it's definitely relatable to to other ppl. Ppl can connect to fantasy characters on a different level than they would realistic characters. And every "realistic" character isn't relatable either depends on the person.
It's not that background doesn't matter it just might matter less in a superhero movie. That's not something particular to superhero movies either. The background setting is always that -in the background. And some movies are more character based where the background isn't that important. Are those movies not cinema?
Ancient Greek epics okay. In some myths Hercules forms the milky way by drinking from Hera's breast, ah the consequences of drinking breast milk.. In earlier versions he's ordered by Zeus not a king to do the labors and they have nothing to do with redemption. So yeah he dies but is reborn as a god. He gets brought back does that invalidate all the consequences he faced? No. But even still MCU chars do face "real world" consequences they just aren't the ones you deem acceptable.
You mentioned Crumb too. Do his char always face real life consequences for their actions? Nope. So by your standard his stuff isn't art either.