I hate it too, but the myth isn’t entirely a wrong. I literally just made a thread about it and how him being a “self-insert” isn’t necessarily a bad thing.
However, Nathanos has definitely become a self-insert.
Let me be clear, it’s not so much that the character himself is a self-insert, but it’s the way that he’s constantly used in the narrative that makes him a self-insert.
He came right the heck out of nowhere in Legion and has since essentially become the new “Nazgrim” for the Horde. He’s a constant presence in Horde questing and is incredibly loyal to his cause. However, the thing that seperates Nazgrim and Nate is the simple fact that while Nazgrim felt like his completely own character with a complete arc, Nathanos exists in the narrative seemingly to constantly blow smoke up Sylvanas’s @$$, to be her personal hypeman and cheerleader. He offers very little else to the overall narrative other than being Danseurs’ vehicle from which he can talk about how awesome Sylvanas is.
Like I said before, Nate has been given multiple opportunities by the narrative to display his individuality, but all he ever seems to do is gawk and throw praise at Sylvanas and how “great” she is. Nazgrim praised Garrosh too, yes, but never to the point in which it defined his character. When we were eventually forced to kill him in SoO, It was heartbreaking because we had quested alongside him and have fought side-by-side for 3 expansions. So being forced to kill him was super tragic. With Nathanos, Horde players could be forced to kill him in the next patch as a quest mob in the War campaign and they wouldn’t bat an eye, because he’s had no major impact on players. All he’s ever done is insult us and mention his precious “dark lady” every other sentence.