Question: What is the scale of the supernatural in your story? Or asked another way, how prevalent is it within the world, and what is the scale of the story in that world? A power will set the MC apart, so you need to ask yourself how do you want that to go? Harry is special because of his power: He was a wizard detective working for Murphy and the other non-wizard detectives. As things developed and the story moved more into the larger Magical community, where everyone was supernaturally special, it became Murphy who was unusual for being in that world and <i>not</I> having any supernatural power. It's all relative. And the larger the gap between his power level and the rest of the
world story, the more burden will fall on you as the author to keep him central to the course of events.
Giving him no power in a band of one trick wonders in a scooby-doo haunted mansion story is easy. Giving him no power in a band of Wizards battling ancient gods is harder, and requires more internal story logic to explain. By contrast giving him the phenomenal cosmic power in a local scale story makes things so easy you have to limit those powers somehow to avoid a Deux ex Machina situation. Along the same vein, if the MC's power level is drastically different from the other two, it will take more work to explain why they are together and what roles/use each one has.
You can make the difference itself become the connecting factor, but you must keep it central to the story. If its something that is only addressed in passing or off-page, it ends up feeling like a bad fit, or worse becomes a central character trait in the readers eyes, and skews everything. If by contrast it's kept central to the story, it transforms from discontinuity to thematic element.
I could ramble on about this for a long time, but thats the basic frame of my thought, without getting into any story specifics