@Harperbows thats probably the reason why the humans left the earth in the first place. And if the mc is that strong as such a skinny noodle then imagine what the trained warriors were like, they probably had enough magic power to contain the power of other humans or just outright deny them power.
Maybe this world is like Jet Li's "The One". the fewer humans on the planet, the more powerful the remaining ones are. And the old ones chose to leave before going all Highlander on each other and destroying the planet with the final battles.