How do you handle powerful characters who limit themselves on principle without being edgy?

Im writing a superhero story where the character in question has incredible power. Yet I'm having trouble trying to convey how they limit themselves personally. The power is something like materiokinesis and ergokinesis. Due to their power, they have an inflated ego and a cruelty streak they keep under control through rules applied to themselves, since they want to live an ideal.

I've already shown how they have a physical limit, requiring focus, a basic idea of what they're doing, and imagination. I've also shown the "rule" they follow either before or after an incident.

What I'm having trouble writing their personal limits without it being a edgy.

For example, they get into a scuffle with a few goons.

The fight is a good old fashioned mob fight. All non-lethal strikes that dont really require medical care. One pulls out a bat so the hero in question responds appropriately and hits that guy harder, breaking a bone. During the fight one of them pulls out a gun and the main character kills them. Fills their lungs with saltwater, their brain to stone, or just straight up makes them disappear. Something with a pang of cruelty.

Does anyone have advice on how to avoid the needless edge?