Still gonna try to 100% the game though. Though I do so with the knowledge that as far as the story goes, what I'm gonna do would be pointless in the end.
Yes and no. The people you're helping aren't going to exist anymore the way you currently see them existing, but consider why Moebius was able to arise in the first place: Everyone collectively feared the uncertain future so much that - with the help of the core crystals they were all stored in - they effectively manifested a god who stopped the future from coming. That fear didn't disappear when our heroes showed up and started kicking Moebius in the strip. Pretty much every colony you do side quests in has some characters that are hesitant to have their clocks smashed because they aren't sure how they're going to survive once the status quo is broken, and the vast majority of side quests revolve around one or more characters trying to navigate the challenges of their newfound freedom. If all you did was stab Z in the face until he stopped moebin, with nothing else done to change the people, there's ample reason to believe that Moebius would just be created again once Origin restarted (heck, there's no reason to believe that cycle hasn't already happened before, but that's highly speculative).
All of those successful side quests help to build people's confidence that there's something better waiting on the other side, even if they can't see it. By the time you finish a given colony's side quests, you've got everyone there on board with killing Z and breaking the cycle they've been bound to. This is why it's so significant that *everyone* joins the assault on Origin: They're all still scared, but they've tempered that fear with enough hope that they're still willing to fight and die for a future that they believe will be better, a belief that will prevent Moebius from arising again. That's an ending the game will give you regardless of how many side quests you do, but where it's left somewhat ambiguous I like to think that doing more side quests helps improve the chances that the cycle gets broken, to the point that 100% side quest completion could be considered canon.
It's also stated quite explicitly that everyone in Aionios is also in Origin somehow, as well as being clearly shown that Origin has stored data on what happens in Aionios (Z's highlight reels, the occasional anomaly like Eunie being able to remember their past lives, etc.). The forms you see the characters in now will cease to exist, but in some capacity the memories of their time in Aionios will persist for their counterparts in the original worlds (all but explicitly suggested by Noah hearing Mio's flute in the post-credit scene). To some extent, the original versions of everyone will remember and/or be influenced by the side quests you did for their Aionios incarnations. The people of the city raise some more questions there, in that there were dozens of generations of people born in Aionios with no obvious counterparts elsewhere, but Melia's comments on the nature of Origin seem to imply that they also have counterparts in Origin, whether corresponding to somebody who will eventually be born (which is weirdly deterministic but not outside of the realm of possibility for a Xeno game) or having been based on the record of somebody already stored there.
It's not "for nothing," but you do have to dig a bit deeper than face value.
T0ffee posted...
Also, side note, it took until the final scene for it to click with me that Lanz was supposed to be a machina. Like all Agnians were Blade Eaters, Flesh Eaters, or Blades; and Keves are Homs, High Entia and Machina. They REALLY changed up the machina designs between the games apparently.
It didn't take me quite that long, but it did take me a lot longer than it should have. The XB1 races kind of play out weirdly in 3, especially as far as lifespans are concerned, and machina are the most egregious example of that.
T0ffee posted...
As for the final final scenes, ehhhhh... Too ambiguous for my tastes, especially comparing it to the clear-cut endings of the previous Xeno titles.
Are they really that much more clear-cut, though? Both 1 and 2 (we'll ignore X because it doesn't have an ending) end with "Well, there's that apocalypse averted, let's all go try to make new lives in this new world," which isn't all that different from how 3 ends. The only real difference is that 1 answers the question of whether or not Fiora survives and 2 confirms that Pyra/Mythra can be (and are) reborn from their core crystal, while 3 leaves its most burning question of "will they meet again?" without an explicit answer (though there are enough hints suggesting that the ending is optimistic that I'd be very surprised if they didn't).
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