To add to what Vhan said, this statement is untrue in a literary sense. Unless you're looking specifically at an underdog type of story, very few beloved characters are plain jane humans with no special powers. Be it in literature, movies, video games, and more. A majority of well beloved characters are exceptionally special. Luke Skywalker is not a "plain jane Human", Harry Potter is not a "plain Jane Human". John Wick, James Bond, Batman, Superman, Spider Man, Hulk, The Master Chief, Doom Guy, Link, all of them have special powers of some sort that set them above and beyond the rest. In fact, I'd go on a limb and say most of them are mary sues in their own little way. But you could never say they're regular Humans, because none of them are. Not a single one.
In fact, off the top of my head, the only character that would come close to being a main character with no special powers is Frodo Baggins. But he's sort of an exception to the rule because the entire point of Frodo is that he is just a regular guy. He is just some regular guy with nothing special about him, that was given the responsibility of saving the entire world, and is surrounded on all sides by insanely powerful heroes and villains. Which is the entire point of that narrative.
And all those powers, or lack there of in the case of Frodo, are used in tandem with their personalities to make each character distinct. Personality is only half of the coin, and the application of what makes a character special is the other half.