The reference with Nguyen is that when you have broken ribs, you shouldn't talk because it's bad for you.

Need a definition of "Mary Sue" to answer the question. Is a Mary Sue a character who is extremely competent? Extremely good? In either cases, yes, but the idea that there's something wrong with writing "Mary Sues" needs to die.

Is a Mary Sue a character who distorts the world around themself, causing other people or the world itself to act out of character so as to implausibly keep the spotlight on the Mary Sue? In that case, there's clearly something wrong with writing Mary Sues, but O-Chul is nowhere near being one.