I don't know if it counts as a dropped plot but Zodiark showing up midway through the story and being controlled by that guy into a swift defeat was lame. There was like an 8 year wait in patch years since the first Zodiark name drop for it to turn out that way.

I would have made him special and titanic in size, so big you can see his movement from space. We would have to travel to different sites across the moon to battle his individual body parts that are trying to break their fetters. There would be multiple sections of him to target and probably adds.

When you've got primal Bahamut razing the realm as a precedent you can't just make the eldest, most powerful primal such a throwaway typical trial. I know he wasn't fully rejoined yet but the ascians were working on him for how many millennia only for it to be stamped out that way.

And yes Garlemald is another egregious example of Endwalker tossing out years of expectations, like 11 years in that case I guess since the empire was a 1.0 thing. Well time travel is a thing now so they could still make Garlemald's glory days into a zone if they really wanted to, just hand wave another explanation.