As an aside, although it still would have been difficult to resolve all of the specific story beats within the course of a single expansion I do think it would have been possible if so much time had not been spend on 'slice of life' scenes between the Scions or suddenly introducing new, never before seen plot points.

I must admit, I was expecting something a lot cooler than Meteion as the cause of the Final Days. I always figured that a good way to make Hydaelyn and Zodiark look better and potentially come together in the long term would be a third party entity to be responsible for the attempted destruction of Etheirys. Some sort of alien/creepy death deity would be a neat nod to the likes of Jenova and Lavos as well as tie in rather nicely with the sinister appearance of Terminus Beasts and Blasphemies.

Would it original? Not particularly - though I'd argue that a little girl being responsible for so much destruction in the story is even less original given that we literally had that same plot point play out during the Nier raids back in Shadowbringers. There's also a certain popular anime that ended recently and chose to attribute much of its story beats to the actions of a sad little girl.