I didn't know who Nubia was until people started talking about her being leaked. And honestly I don't mind that. When I played Smash Bros for the first time I only knew the Pokemon.
I'm more interested in seeing how a character turns out before writing them off. A "literal who" is a new face to learn about and see if I like, not an immediate dismissal, though I do understand that I'm in the minority in that regard.
From a marketing/dev angle though I do have to agree with the criticism though.
Multiversus is plagued with lots of problems, and while not a solution, adding big name characters are at least a means to keep some player retention or bring in new players who like x or y character/series enough to give MVS a spin.
Tbh, I think MVS is objectively pretty bad in its current state. I want it to bounce back and succeed but they've got a long road ahead of them with a limited amount of time and the big obstacle of their own publisher/parent company likely enforcing a lot of the poor decisions everyone keeps complaining about.
All that to say, that while the roster lineup and release schedule could be handled a bit better, I don't think it'd be as big of a problem if it weren't for literally everything else that the game is lacking and/ or needs improvements on.
Personally, I think the game feel, balance/bugs, lack of content and predatory monetization are much bigger problems that need to be addressed first.