I just don't think the Piper of Dreadnought!
fits enough of the diagnostic criteria for a Mary Sue to qualify -- althoug the Piper of Battlestations!
might, given how swiftly she's been promoted in rank and become a member of Kirk's inner circle. In Dreadnought!
, at least, she's not smarter and better and more successful than the leads -- indeed, that's the entire point of her character in that book, that she's far, far behind Kirk in her ability and experience, even if she has a potential comparable to his.
And I don't accept her central role as making her a Mary Sue, because she's just the lead of a whole ensemble of lower-decks characters, rather than a single standout guest star. Why is she a Mary Sue if Sarda, Merete, and Scanner aren't? Sure, she's more central to the book, but what else could a first-person narrator be?
The one criterion I'll grant is author insertion, but that by itself does not make a Mary Sue. There have been some great author-surrogate characters in fiction.