Seriously?
Let us look at Deep Space 9 since you're currently watching that. Sisko is awesome, but is he REALLY the most interesting character?
What about Voyager? You're saying Janeway topped the Doctor and/or Borg in interest? REALLY?
Most interesting? Dunno about that, but, there's no doubt that the series definitely places him at the center of the story lines. As it does with Janeway as well. Is there any real doubt here that either character is the main protagonist on the show?
Here are two characters that get the most screen time overall, and whose decisions and actions drive the plot for pretty much every episode. Sure, there are a few episodes every season where the captain isn't at the centre, but, that's because you'Ve got 24 (ish) episodes per season. You can afford to have that.
And that youtube video was pretty much a selection of bog standard clips about the protagonist in a Star Trek serial. You could make identical, almost scene for scene clip collections for Kirk or Picard. Youngest captain ever. Top of his class. Most decorated Star Fleet captain ever. Loved by every alien female. Oh, but, Kirk's not a Mary Sue. Picard is pretty much in the same boat as well. Best captain. Moral center of the universe. Never mistaken.
Look, I get criticizing Discovery, I really do. But, these Mary Sue things are bizarre considering what we're comparing Burnham to. It really does ring rather false.
IOW, "I don't like the character of Burnham, I find her unbelievable, flat, two dimensional and kinda boring" is an arguable, but, understandable point. "I don't like Burnham because she's a Mary Sue" just invites all sorts of counter arguments that reveal that no, she really isn't.