FWIW, broken stories are broken, and that makes them irrelevant here. (Though, not irrelevant in a larger scheme, just not when talking about structure.)
I don't remember the movie all that well, but that is not what I see here. I'm building on this and:
Basically, I think people are mistaking well-drawn characters and exciting characters that get our adrenaline and interest up with Main Characters. (See Dead Poets Society for another example of this.)
Main Characters have a unique perspective and get us emotionally involved with their journey. Well-drawn characters certainly get us involved, and we get them, but it's different.
That's not to say that authors can't decide to let you in and treat a character like an MC for a moment. For instance, the
IC in Frozen, seems to be saying "Hey, that paradigm you use where you really only understand the inner workings of the MC... Let It Go for this song." Or, in maybe the 3rd or 4th episode of The Wire we get a very MC-like treatment of one of the policewomen -- which bonds us to her, which the writers take advantage of a couple of episodes later. (Trying to avoid spoilers here.) But she's not the MC writ large, just for a tale we never get more than a small taste of.
But I do think what they do in The Wire is different from what they do in _Pirates of the Caribbean.