Contains spoilers for Shadowbringers, Endwalker, and the Heavensward Alexander raids.
You know how everyone always says that time travel rules in FFXIV are “inconsistent”? Well, they’re not!
The Alexander raids are one big time loop, leading many to conclude that time travel in FFXIV must result in a self-consistent timeline. But remember what Dayan told Mide?
From this place — unfettered by the mortal construct of time — Alexander looks out upon past, present, and future, seeing infinite possibilities. […]
Oh, if you could see the worlds we have seen! A world in which the Illuminati rule history with an iron fist, every nation brought under their yoke. A world in which Alexander spread wide the wings of time and swept the lesser moon from the heavens, averting the Calamity…
Alexander dreamed all the realities imaginable — all the realities mathematically computable — and in the end, reached a single, logical conclusion. It would change nothing, and erase itself from existence.
Alexander possesses the power to travel through time and space, and reshape history for the better — but such power comes at great cost. The sheer quantity of aether consumed in the process means that Alexander would — mayhap not immediately, but inevitably — bring ruin to this world. This perfect machine, this supreme manifestation of logic and science, deemed its own existence a threat. And so it chose to do nothing. To leave history untouched, and the future in the hands of man, with all his imperfections. Such was Alexander’s divine judgment.
tl;dr… Alexander could have changed history. It deliberately chose not to.
Yet Alexander had to exist, at least for a little while. There are two reasons why, both answered in Shadowbringers.
The first, most obvious, reason is because the Garlond Ironworks of the post-Eighth-Calamity timeline needed the knowledge that was recorded from Alexander in order to send the Crystal Tower back in time to the First.
But why was this necessary…? This is still changing history, and so it’s a drain on the land and a risk, isn’t it? Perhaps Alexander decided that this was a necessary trade-off. Or perhaps it was an unavoidable consequence of the least invasive timeline Alexander could compute. I think there’s another possibility, though, and I’ll come back to that.
The second reason Alexander had to exist? That’s answered in the Tales from the Shadows short story, An Unpromised Tomorrow — albeit indirectly. This is the story of the Garlond Ironworks from the alternate future of the Eighth Umbral Calamity. After they send the Crystal Tower away, someone wonders, “Will we be disappearing too?”
But they don’t. They, and their timeline, continue onward.
So if Alexander had created a timeline where it had never existed, that wouldn’t mean anything for the timeline in which it was originally summoned! It would be an alternate timeline, like the Eighth Umbral Calamity timeline was. And it would probably be great if the world of that alternate timeline didn’t suffer any drain on its land’s aether from Alexander’s brief existence, but it wouldn’t solve the problem at all.
And now we come to Endwalker, when Elidibus uses the power of the Crystal Tower to send the Warrior of Light back to the World Unsundered. In doing so, he tells us,
In all likelihood, none will be able to see or hear you. Yet even should you manage to interact with others, you will be unable to effect meaningful change. For the reality you wish to save—the reality to which you must return—exists as a result of the Final Days.
You cannot reshape the past to undo the tragedies of the present. Cannot unmake the sorrow and suffering fated to come.
Does this contradict what the Crystal Exarch did to avert the Eighth Calamity? I don’t think so. Because he didn’t prevent the Calamity in the timeline it actually happened in; he just kept it from happening in a new timeline, our timeline.
Elidibus even says it himself: The reality you wish to save. Our reality, the one we live in and will return to when we’re done in Elpis.
Could we have stopped the Final Days when we were in the past? Maybe, but it wouldn’t have done a thing for the present. (There also would have been implications for the Pandaemonium raids.)
You can argue all you like about whether we should have had the option — I think it would have been nice to save an alternate timeline, personally — or whether the KAIROS thing was just needlessly contrived, or whatever… but for all the flaws the storyline may have had, I firmly believe the time travel aspect, at least, was completely consistent.
Oh, and just one more thing: That pin I stuck in the topic of “Why did Alexander allow for Garlond Ironworks to use its technology to send the Crystal Tower back in time?” If it hadn’t done that, we couldn’t have gone back to Elpis and contributed to the closed timeloop there. Alexander truly did have the biggest brain.