Very well said, thank you, and I'll be pondering it. I hadn't really considered the universe-warping aspect. But you're absolutely right. I was around in the 70s when Paula Smith coined the term, and it referred specifically to characters inserted into ST:TOS fanfic.
For me, Mary and Gary have been one part "appears to have things in common with the author" and five parts "way too perfect to be believed". I have, to cite the most recent time I've used it, described the protagonist of Scalzi's Old Man's War as a Gary Stu.
I would never describe one of your characters as a Mary or Gary, simply because an essential part of the definition for me is "never, ever screws up, or does anything for the wrong reason", and I've never seen you write that.
no subject
For me, Mary and Gary have been one part "appears to have things in common with the author" and five parts "way too perfect to be believed". I have, to cite the most recent time I've used it, described the protagonist of Scalzi's Old Man's War as a Gary Stu.
I would never describe one of your characters as a Mary or Gary, simply because an essential part of the definition for me is "never, ever screws up, or does anything for the wrong reason", and I've never seen you write that.