I find the discussion around the game being finished or not a little bit tiring to be honest. The game is a large package of content with interesting story beats spread out in it, and most importantly very satisfying combat.
I don't think anyone will disagree that the game's story is not the most coherent it could have been. However, this should have been fair obviously from the fact that the game represents a compression of a trilogy; condensing such a story would inevitably lead to characters and location being shafted. The strange thing in my eyes is that even areas like Tenebrae that were fully shown off in pre release were so clearly cut from the game yet still used to fulfill the promise of it being there. The character of Rafus is also bizarre: he appears like four times or so, once in a cutscene with the empire, once holding the bros at sword point, once I a cutscene with Luna talking about her illness, and for the Last time in Chapter 13. Why anything happened to him is completely left out. Furthermore, Luna's journey is one that happens completely off-screen, which made her scène about her illness and her final appearance in Chapter 9 feel disjointed. Not to mention general Verstel who appears exactly once in the whole game, or the empire who also appears once: they clearly had a lot more story in there that got cut in the transition from VSXIII to XV.
I think denying that the game has missing development for several characters and story aspects is unfounded, but I also think the claim that the game does not hold up on its own as at least a serviceable story is unfair. The story, though strangely paced and abrupt, is still understandable at least to a certain degree, and though it will not win awards for its story, the game has a serviceable tale that sometimes shines, for example in Chapter 9 and in the ending. Along with that, the game does a good Job of characterising the four main characters and to give them their own personality. In that aspect, they definitely succeeded in my eyes.