Zenos' death was not only pointless, it shoots Endwalker's central theme in the foot and makes the moral fall flat.
The entire theme and "moral" of Endwalker is that life, despite all its hardships, is still worth living, and even if despair is inevitable, that you should never give in to it, to always have hope and forge ahead to make your own path. This is the lesson that the WoL has learned over the course of the story, and it is the lesson that they teach to Meteion at the end.
Zenos ties into this theme in a really interesting way, because when we meet him again after Elpis, he basically states it word-for-word as his own mindset, that there is no inherent "point" in life and therefore everyone must find their own purpose, as he has. This very mindset is what makes him immune to despair. Of course, Alisaie then rightfully points out that while that may be true, his refusal to listen to anyone else is ultimately going to lead to him never getting what he wants, and dying alone.
And Zenos listens. And that's where it falls apart.
Zenos genuinely takes Alisaie's words to heart, and changes for the better. He approaches Krile in Old Sharlayan and (though we never see the conversation they had) they "strike a bargain," rather than him taking the Mothercrystal by force. He flies to the end of the universe to help the WoL against the Endsinger, saving the universe by their side. And then, after the WoL finishes telling Meteion about how beautiful hope is and how living is important, Zenos has a heart-to-heart to WoL wherein he speaks to them as an equal and even says they can refuse him if they wish (even though the player can't).
And then, after we JUST finished delivering the moral to the sad bird antagonist, telling her that we must never give up on life... Zenos dies, ultimately having realized his life was unfulfilled.
Some might say "but wait, he got what he wanted and died happy," but I would ask them to watch his final scene again. He says that the battle was what he wanted, but that the joy it brought was only fleeting, and not true fulfillment. He asks the WoL if they managed to find fulfillment in their own life, unlike him. In other translations this is even more obvious; in the German dub he even outright says "your life was so much better than mine." He starts to say something else... and then stops breathing. And WoL is whisked away by the teleporter.
So despite listening to Alisaie and changing for the better, Zenos' ultimate reward for his character growth is STILL to die alone at the end of the universe, coming to the realization that his life was empty, AFTER WE JUST GOT FINISHED TELLING METEION THAT LIFE IS WORTHWHILE. And the reason why I keep pointing out that his death happened after the conversation with Meteion is because the timing is what really throws the moral out of whack. By telling Meteion about hope and the necessity to not fall to despair, then killing Zenos minutes later and having him lament the emptiness of his own life despite him being the other person who helped save the universe, after having literally stated the central theme of the story is his own ideology, it's as if the narrative says "everyone needs to find their own purpose in life and forge ahead, to find hope even in their darkest hour, and that's what will make their life worth living... except for this guy, f*ck him."
It would be one thing if Zenos was meant to serve as a cautionary tale in the greater context of Endwalker on how forging true connections with others helps us carry on; for example, if he had been told way earlier in the expac that he needs to change, and he had refused, instead insisting on his own selfish desires above all else and then dying before Ultima Thule, his death would be a fitting warning, especially amidst scenes like the people of Thavnair helping each other and supporting one another, and the Scions sacrificing themselves one-by-one to form a path for the WoL in Ultima Thule. His death would tell us the importance of the relationships the WoL has forged, and where we might be without the friends we made along the way.
Instead, he changes to help us, yet mere minutes after we see Meteion off as she learns not to give in to despair and to love life, Zenos is punished, and for what? Why is only Zenos left out in the cold?
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Anyway I have many MANY more thoughts about how poorly they've handled Zenos, but this is already too long. Admittedly this also worries me because the devs have said before that they were planning on having a Garlemald expansion pack between ShB and EW, with Anima as the final boss, but decided to skip right to EW. When that is taken into consideration with the timing of Zenos' return at the end of ShB to his role in EW, it becomes clear that Zenos was meant to have a bigger role in the nonexistent Garlemald expac, which is why they never answered any of the questions raised about him in the ShB patches, such as why he has dreams of the Final Days. There's so much about Zenos that remains unanswered, and to completely abandon him as a character and never resolve those plot hooks because YOU CHOSE to cut the expansion pack where he was going to be important...
I don't hate Endwalker, but I think it has some really high highs and some REALLY low lows, mostly due to wonky pacing.