@SleepingSilence Mary Sues in roleplay are gorgeous because they're created by the audience as representation of themselves, whereas in films and books the Mary Sue is presented
to the audience by an outside party, usually for a solitary story beat (power fantasy, steamy romance, w/e). In the latter case, averageness is more relatable because the audience is entering a world over which they have no creative control, with which they're unfamiliar.
The fantasy is the audience themselves entering the world through a sympathetic vessel.The first time you pick up a book series you have probably had no exposure to that fictional universe's laws, folkways, customs, and cultures before, and while a "fish out of water" is a perfectly acceptable device for introducing the audience to this world, the Mary Sue is a character who, while living among all these rules, can ignore them or even be
ignorant to them at will, entirely without repercussions. Among these rules of course is beauty standards, and if a character can be lusted over by all cast members of the opposite sex despite not deserving it (being "average" and not, by that culture's standards, a near-perfect physical specimen), then they have broken rules of their own universe without consequence. Therefore they're still Mary Sues, despite what the author says about how "plain" they are.
That's the difference. When it comes to middle-aged housewives and 12 year old pre-teen girls watching a romance movie, which is the better fantasy? Hot guys swooning for a busty supermodel who looks nothing like them, or hot guys swooning for an average chick who kinda-sorta-maybe looks like them, and could some day
be them in a romantic encounter at a restaurant or something? Whereas when
you're the one writing the fantasy, of course you'd be as beautiful as possible, because beauty brings with it more power than just sexual desirability. It has more utility in RP and it's simply more fun (*for these people, not for me) to pretend you're beautiful and not normal, since you're already normal IRL.