All protagonists from all shows save the day on the regular.
But at least with the other shows, saving the day is rotated amongst the rest of the cast. Deanna Troi saved the day several times. Even Harry Kim got to save the day multiple times. Hell, Mayweather got to save the day a couple times.
With Burnham, it seems like it is mostly her. I get that she's the captain and the buck ultimately stops with her, but spread the wealth a little bit. When Harry Kim saves the day more than all the regulars on your show put together, that's a monopoly on day saving. So yes, in that way, I think she can be called a Mary Sue.