Whatever adjective makes you feel better: appropriate, apt, fitting, correct, modest, less expansive, less assuming, less imperious, less opulent, less grandiose, less egocentric, less narcissistic

The point you’re trying to make is correct on a technical level, not a functional one. Unfortunately we can’t will languages into behaving in ways we think is ideal simply by making pointless assertions in obscure forums.

And I guess South African should be something else, because there are other states in southern Africa? Language doesn't really care about being "correct" with terms. It cares about being understandable. No one knows what USAian is. Everyone knows what American is. There isn't really any debate anywhere around what to call people from the United States of America, even among other American nations.