Well, there's another direction to think in - how do you put the fantasy in superhuman fantasy? Sure, you can explore the sociology of people with superpowers to get the broad mechanics of how the settng works, but what makes it memorable is the themes that filter down through the specific details. I also think a degree of mystery and ambiguity (though not too much) can be beneficial.
For one I'd have there be setting elements that hint at stories for where superpowers come from, but which are contradicted by equally compelling alternatives. If some people think superhumans are the reincarnations of gods and demons, well, maybe there's more than superstition to support that idea. Maybe someone claims to remember their past life as a god-king deva and they're digging up ancient ruins to regain their old regalia. Are they alien hybrids? Same, but the ancient ruins are full of strange metal objects. Are they the next rung of spiritual evolution? Perhaps there's a monk who awakened theirs using meditation, or a mad scientist who used drugs and surgery. Are they parts of a greater whole? Some superpowers combine together in unexpected ways.
One big thing you can do is reconstruct fantasy tropes using the mechanics of superpowers. Worm did this all the time, with Lung the Dragon and Ziz the Angel and Nilbog the Goblin King and so forth. You can throw in some monstrous threats as a background to human vs. human conflict, whether it's people who got mutated by their superpowers until they don't look or think human anymore, or things that got created and went out of control. In most fantasy settings the wilderness is full of danger, after all.