I mean I take it the same way I've looked at KH for a while now. Sora is simply the POV character, but he's not the primary character. Riku, Terra, and Aqua are the primary characters that have a driving protagonist role in the narrative.
Most people disagree but I think it squares pretty well with his basically inconsequential Sora is to the actual stuff going on other than being the hiding place for like 15 other people's souls.
And yes, it should 100% have been Terra fighting MX at the end with Sora playing support. Or the Destiny Island trinity doing the first and second phase while Sora/Donald/Goofy for the last phase because that's the real "trinity" of the games which helps tie it together in a nice little bow.
I don't think it was bad how they ended up doing it, but it could have been done much better and more resonant.
I just think it's a weird angle to take for a character like Sora that actually has his own personality and motivations. This is usually the type of thing a silent protagonist or something does and I don't really like it there either.
I think the PS2 games were pretty focused on Sora or at least characters in his immediate circle but this feels beyond him. Hopefully the next game gives us something a little more personal.