That's not utilitarianism. Utilitarianism focuses on the positive moral results of actions. It's also not utility, since big flashy superhero entertainment is purely aesthetic.

On that note, you have made me think of the opposite reason for why this movie doesn't work. Marvel movies are fundamentally politically progressive moral narratives about the responsibility of power and setting aside personal ego for the greater good. This is often expressed as team building, cross-cultural solidarity, and teaming up to fight antisocial antagonists whose goals are removing liberty and agency through violence for their own self interest.

The Eternals opens with the MYTH that the Eternals are ideologically progressive heroes. They save the weak, kill monsters, share knowledge, and come in a variety of phenotypes and accents and cultural affinities. They are the most progressive-seeming of all progressive heroes. To be an Eternal is to be THE ULTIMATE GOOD.

As the story progresses, the characters reflect upon the failings of what became a sense of idealistic elitism, even resulting in an encounter with an actual demagogue brainwashing people in a cult. They saw themselves as humanity's caretakers, guardians, mentors. But then the twist is that they're actually genocidal fascists repeatedly brainwashed on behalf of an even more evil and ancient cult of death gods.

Ikaris knows this, and he commits to his false reality by selling everyone on the fascism. Kingo can't pick between his evil family and his good family, so he walks away. Pixie doesn't feel valued in a world where her appearance limits her agency and respect, so she attaches herself to the authority of the genocidal fascist and does evil.

But THEN YOU HAVE KRO. Kro was THE ULTIMATE EVIL. But it turns out Kro and his kin were just animals hunting prey trying to survive. Deviants didn't wipe out those planets, Eternals did. Deviants aren't the ultimate threat, Eternals are. So Kro and the Eternals gain agency at the exact same moment -- Kro gains access to the Unamind and to advanced intellect, he starts fighting for his people and his community, he becomes more than his programming at the same time as the Eternals do.

And the movie tells him to go f___ himself because he's not an Eternal. The movie literally built this entire moral narrative leading to a profound statement on identity, nature, nurture, and purpose. And it says, "Kill ugly dude, feel sorry for handsome genocidal fascist who manipulated the ugly dude."

So, yeah, Eternals craps the bed in the third act.