I definitely have a lot of critiques about how the story was handled, too, and could go off on a rant. They did get more ambitious with regards to the spectacle of the climax, but storywise I think there's a really jarring sense that Taunie/Urbain was originally meant to be more complex and have a more interesting role there but then they backed out of it and left it kind of incoherent. The way Taunie acted about climbing the tower - insisting on a battle for who gets to climb the tower, her very specific character animation at the start of the battle making it look like this is the most important thing in the world to her, then insisting she be the one to go anyway when she loses, all make it look like she has some very specific meaningful private reason she's absolutely determined to be the one going up in the tower... but no, it turns out there's no real significance to that, other than that it means the endgame sequence can involve you not going up in the tower at all after the player has probably been anticipating they would this whole time. If they'd just meant to have Taunie climb the tower from the start, then they wouldn't have had to had this whole battle against her about it to begin with - they could've just written the story so that the decision Taunie climbs the tower and you try to find Zygarde was the plan from the start!
I thought for a bit that what they might be doing with that was that because of something involving Taunie's established dead mom and "looking for someone", she was determined to take control of the tower, to use it for some misguided purpose (revive her dead mom?), and she'd be the final boss, fighting against you using the tower's power. We even see her go up in the control room and put her hand on the control panel, as if she's about to be the one in control... but then no, we get no more cutscene from her point of view, just dialogue saying she's fine and Floette is protecting her and you should go find Zygarde. I thought she might be lying and trying to get us to just go as far away from the tower as possible so she could do her thing! But nah. All in all it would have been so much more interesting and I can't help but think it originally was more interesting and then they rewrote it clumsily.