Burnham who was arrested for mutiny and stripped of her rank? She just gets everything right, doesn't she?
But we know that she was right, right?
I mean, being unappreciated and misunderstood by those around you can be a facet of MarySuedom, as can be dealing with the jealouses and unfair treatment at the hands of other characters.
In the end, though, Mary Sue is rewarded with public applause and appreciation by those authority figures and peers who misjudged and underestimated her in the beginning.
Okay, I really totally agree that Burnham is not a Mary Sue. But it is difficult to reason one's way out of that bag when, as you noted, the character is the heroic center of a fantasy story like this. What DC superhero couldn't be branded a "Mary Sue," after all?