If memory serves, I think the DISCO creators had been transparent about their series being principally about Burnham and her journey. And there’s nothing wrong with that. It was doing something different with the Trek formula and not that dissimilar to what other television series do (and new Trek did further by even naming a series for Picard). To me, it was a more explicit way to structure their series than the implicit captains as leads of prior Treks (and with stronger ensemble casts in the Berman era).
Perhaps, the DISCO brain trust was thinking that it would be easier for newbies to get hooked into the journey of one character as opposed to an ensemble. And with that said, while I do think overall ensemble character development has been wanting, it has been improving. Even in the first season, other characters besides Burnham got some spotlight. I don’t agree with the idea that Burnham was a flawless character that got EVERYTHING right. Right off, the pilot episode showed her getting things very wrong, and by the end of the second episode, she had helped abet a war, got her maternal figure captain killed, and been court martialed. A large part of the first season was about Burnham redeeming herself. Even in the fourth season, she was often at odds with the Federation president, so Burnham, despite her gifts, and DISCO’s propensity to prove her right in the end (or get the win) doesn’t get to skate to the winner’s circle.
It's funny that there are no complaints when "Non-Diverse Males" like Archer, Pike, Kirk, and Picard often get the wins as well. If they don't get the wins, some might gripe that that is "woke" deconstructionism of "traditional", "classic", and "iconic" characters run amok.