I speak as a writer here, not a comic artist, but I think my points still stand in all mediums of work.
Now, I have a lot of very powerful characters. Alpha-7 can lift four tons, Tatakai is insanely powerful, Crypto’s literally immortal.
But they’re always nerfed by their personal struggles. Alpha-7 deals with rising questions of their sanity and the struggle of living in a world of eggshells, Tatakai’s intelligence poses so many problems she wishes she was born smart instead of strong and Crypto feels depressed and isolated from everyone around him.
The way I see it, a character becomes a Mary Sue not when they have powerful abilities, but when any personal struggles they have are easily solved, when they’re always in the right and when everyone around them sees them as incredible no matter what they do.
The biggest challenge when writing an OP character is making them still relatable to the audience, I do this by focusing on their mental health and making their personal journeys about improving it and taking care of themselves. It’s something of an iconic trend in my work, at this point. Even the comparatively weak MCs’ personal arcs are focused on their mental health.