Wikipedia: “In fan fiction, a Mary Sue or, in case of a male character, Gary Stu or Marty Stu is an idealized character, often but not necessarily an author insert and/or wish-fulfillment.”
Humans – In many works of science fiction and fantasy in general they could be considered the Mary Sue race, in a special way, through relation to others. (Because as soon as there is a race that puts humans to shame, the common definition wouldn’t work anymore. But such a race could still be a clichée. I just couldn’t find a better way to name this trope.)
I understand that often alien races are a tool for reflecting certain human traits for closer examination and exploration of specific aspects, e.g. for showing us the mirror, but it can also be considered lazy writing and could even fuel a certain hubris.
Did you notice how other races are often just a sub-section of human cultures/psyche/behavior etc.? People would ask things like “What is this race like?” Imagine an ET visitor asked you to tell him what humans are like, what kind of a species they are. Weird question, isn’t it?
It reminds me of how in Star Trek they eventually loosened that view and fixed some of the clichée when they revealed that “warrior Klingons” was just the generalized assumption because Starfleet had mostly just interacted with their military and thus in their narrow-mindedness probably never have considered that there are wise, peaceful Klingon teachers and all kinds of people like that. In a way, here the evolution of Star Trek lore over time serves its own exploration of human nature and our experience of life.