> People usually become billionaires via having “super-powers,” i.e., very unusual abilities, at least within some context.

If you count luck, maybe.

> But what if most billionaires had super-powers of the traditional comic book sort, like x-ray vision or an ability to fly, etc.? That is, what if people with physical super-powers earned billions in the labor market by selling the use of these powers? Would folks be just as eager to tax them to reduce unfair inequality?

Yes, I would.

> But if those few very rich folks had real physical super-powers, we would be a lot more afraid of their simple physical retaliation. They might be very effective at physically resisting our attempts to take their stuff.

Yes, and this is why a lot of superhero movies involve fighting the greedy superpowered villain.