Revelation about the universe (SPOILERS)

[Lauront]

The ancients are closer to dragons opposed to..? Us? The comparison being made was to us, humans and mankind as it exists in FFXIV. I think what you've done is point out similarities between the Ancients and the Dragons, which is fair. Yes, they all do share some human aspects. But a lot of that has to do with as humans, we have the ability to recognize traits in others that are humane. However, something else all of these beings we witness between Elpis and Ultima Thule have in common are their extremely long lifespans, and that their respective civilizations were around for much longer than the time Etheirys has been sundured.

The game points out on several occasions the inability of our antagonists to see life as we do. It is the crucible where our conflict takes place. A fundamental block that is missing for them is indeed the short lifespans of the sundered. This serves to only confuse them, as you have pointed out with the quote from Eldibus. They just can't grasp it, when the answer is right in front of their face the whole time. In my opinion, despite their rationalization behind their actions, both Elidibus and Emet are fully aware that the genocide they desired to bring about is wrong. Their enthrallment with their God has them act in contrast to that, but the duties their seats hold in the convocation can be seen as reasons as well, just to lesser extent.

But it's not just their lifespans that are the issue for them - it's the fact that the sundered are the result of fracturing their star and people and creating out of that something unrecognisable to them - different to the extent that their lifespans are significantly reduced, the loss of the ability to use creation magicks, the echo reduced in what it could do, etc. It's clear some of them, like Emet-Selch, do feel some discomfort with the rejoinings (his perspective on the sundered is suggested to have shifted over time to seeing them as nearer to child-like beings), but it is ultimately genocide in answer to the genocide of their kind, to reverse it. While the game does point to their different perspectives on life at various points, it is emphatically not doing so with Elidibus in SoS.

At that juncture, the character is trying to demoralise him, and Elidibus is reaffirming his resolve, in spite of his memory loss - the entire point here is his commitment to his people and willingness to fight to see that through to the end. Moreover, the game goes to no small amount of lengths to parallel Elidibus's resolve to the Exarch's, i.e. here:

What will you say?
1) Why me? | 2) Did you never consider other paths?
1) Crystal Exarch
Why you? Why not you? Had I chosen another, we would never have made it this far. Or do I mistake your meaning...?
2) Crystal Exarch
I did─but I chose not to walk them, thank the gods. Why ever would you ask me such a thing?
Crystal Exarch
...Elidibus spoke in similar terms, you say? How curious.
To answer your question, then, I made my choice for reasons which seemed obvious to me, but may not to any other.
There were the expectations I placed upon myself before beginning my slumber. And the expectations of those who roused me.
Of course, I had the choice to turn my back on the lot of it. But in the end, it was no choice at all.
I cherish the time I spent with you and the others. What I wouldn't give to return to those halcyon days...
Chasing ancient secrets, overcoming trial after trial with the aid of like-minded comrades...
And what remarkable comrades they were. In such company, I felt as if I were a character in the epic tales that had stirred my heart as a boy. As if my dream had come true...
It hadn't, of course, for I was no hero. Neither then nor after. Though the world to which I awakened, and the First were beset with myriad problems, I rarely knew how best to play my part.
There was, however, one thing of which I was certain: that I could not bear to let those dear to me meet a tragic end.
I'm afraid our time is up. Go.
Rest assured you haven't seen the last of me. I wouldn't dream of playing my trump card save in your presence.

This is directly paralleling Elidibus's devotion to his duty and his people. So again, I would say that both from his and Emet-Selch's own resolve, we can very readily argue that the ancients did understand life in the sense of the importance of fighting to preserve it against a premature end. Indeed, the entire Ascian struggle is to undo that end. The reason I brought up the dragons is because they're most comparable to the ancients in their span of powers, lifespan and defiance against a fate that would see them destroyed - all of which they do in spite being very long-lived beings.

As for tempering? There's a number of problems with arguing that it directed their actions in service of their cause. First and foremost is that Zodiark's tempering is the result of the power that went into his summoning (see here for where this is implied.) The primal itself lacks the usual will primals do outside of its heart, and Emet-Selch himself is able to simply deviate from that path. Zodiark's return is in service of restoring the star and returning their people. All in all, there isn't enough for me to say it's what's the driving factor in their motivations.

Based on the lore we know, their tempering consists in alignment to the primal's aether, and yes, as per Emet, a desire to spread this aspect. It can evidently degrade memory and identity if those are not actively preserved (which Emet-Selch went to great lengths to do), but in both Emet-Selch's and Elidibus's case, they are strongly characterised as driven by their duty to their people, which Emet-Selch only forgoes because he lost (he even reaffirms this at the end), and likewise for Elidibus.

The ancient that comes to closest to having the same or similar concept of life we do is Hermes. I think if there is a comparison to make between ancient and man, he would be the best example to use. This is of course, prior to Meteion's report.

I am not bringing him up here because he is not relevant to the point of the acceptance of an "inevitable end", which was the point you raised in differentiating immortal races from those which are not. On that front? He in fact struggles to see purpose in life when faced with death as its eventual companion.

I'm not sure he decided to rest so much as we defeated him and his resolve to restore the unsundered. Ultimately, the ancients are devoted to the star and its survival. I would say Hades did finally accept his return to the star, and prior to doing so places his faith in us to defend Etheirys.

Different ways of saying the same thing.

The ancient that had to endure this absolutely frightening fate was Venat. Armed with the knowledge of the final days, she could do nothing to stop it. Even if Meteion showed up and offered to spare Etheirys, Venat would've had to decline it. This is SOOOOO much worse than what I was talking about. My goodness! Poor, poor Venat

Poor poor ancients in general. The entire event was traumatic to the extent that it was seared into their memories such that even within the sundered, it can be reignited with the right trigger. Imagine then being the three survivors who didn't even have this context and then witness on top of this destruction, the fragmentation of their world and people, for reasons they were never given... it's tragic for all concerned.