When are we supposed to stop fighting?

[Lauront]

The Final Days didn't warp their creations into Blasphemes. Rather Terminus Beasts were created through their magic being forcibly usurped and the concepts being siphoned from their minds against their will. The quote you posted is nothing but speculation of how it might work, and note that it's not saying that it afflicted their creations, but rather their magicks themselves.

Yep and it fails to account for how dynamis would even affect them to put them into a state of despair in the first place if it were not possible at all. The natural conclusion here is that the transformation is what their denser aether inhibits. We see the creations discussed here even before the incident spread like wildfire to the point that mass panic occurred, as incidents of "spontaneous creation". My guess is that that "readily" Hermes specifies is meant to be taken in conjunction with both the ability to manipulate dynamis, and to be affected by it, because the latter quite clearly is possible through rendering them in a state of despair in the first place. Indeed this is how it reads in the FR version, where it simply premises it as interaction with dynamis becoming easier if the aether is thinner.

Meanwhile the shade's description on it is emphatic:

Have you not heard? Though yet confined to the lands across the sea, a terrible phenomenon afflicts our star. They are calling it the “Final Days.”
'Tis said it starts suddenly, a cacophonous keening from beneath the earth. The sound distorts all living things within earshot, and wrests from us control of our creation magicks.
Once that happens, all is lost. Fear, pain, despair...every dread impulse is siphoned from our minds and given substance: an eternal fall of fiery rain; an incessant spawning of nightmarish beasts...
None can point to the source of the phenomenon. 'Tis as if the star itself has fallen ill─as if a force inimical to life now festers and spreads.
'Tis only a matter of time until Amaurot, too, resounds to that discordant squall. You should stay with your loved ones, child... Stay with them...

So I think that quote does not make the point that their creation magicks could not be affected (indeed, his own words contradict that) - all it seems to be saying is that it did not affect their bodies (and souls?) wholesale via transformations because of their denser aether. Emotional states, and yes, seemingly even control over creation magicks, could be affected. The ancients already knew they could accidentally create things sometimes (underscoring once more how natural this ability is to them) – so I doubt the loss of control would even have been seen as noteworthy if it were not for the precipitating factor (=keening) that led to it, as opposed to the usual accidental use of such magicks in situations of panic, shock etc. You could just drop it and attribute the loss of control to the despair - yet this isn't how it's described at all, hence this loss of control seems to be pivotal here as a differentiating factor.

The subterranean keening aspect appears to remain unexplained, and perhaps Pandaemonium may touch on it. The 1.0 CNJ quests detailed similar events with the elementals whereby their wrath results in a keening and they seize control over the will of man; the game is silent on the role of the elementals in the ancient world, to the extent that they even existed and, if they did, how they’d react to a sustained onslaught of despair beyond the rather ephemeral Final Days the current timeline saw. Possible red herring but I find it interesting.

[KageTokage]

The subterranean keening aspect appears to remain unexplained, and perhaps Pandaemonium may touch on it. The 1.0 CNJ quests detailed similar events with the elementals whereby their wrath results in a keening and they seize control over the will of man; the game is silent on the role of the elementals in the ancient world, to the extent that they even existed and, if they did, how they’d react to a sustained onslaught of despair beyond the rather ephemeral Final Days the current timeline saw. Possible red herring but I find it interesting.

I kind of feel like that's a plot thread that they might latch onto going into the future, because there was a noticeable lack of the natural disasters that were tearing the world apart that were present with the original Final Days, which to me suggests they might've been coming from somewhere else. Either things simply didn't progress far enough to trigger them, or worse, we haven't actually seen them manifest yet.

The prophetic words of the Golden Dyhata suggesting the Lifestream itself will eventually be responsible for widespread disaster is something that raises particular concern to me.

[RyuDragnier]

I kind of feel like that's a plot thread that they might latch onto going into the future, because there was a noticeable lack of the natural disasters that were tearing the world apart that were present with the original Final Days, which to me suggests they might've been coming from somewhere else. Either things simply didn't progress far enough to trigger them, or worse, we haven't actually seen them manifest yet.

The prophetic words of the Golden Dyhata suggesting the Lifestream itself will eventually be responsible for widespread disaster is something that raises particular concern to me.

I feel the same too. If Pandaemonium does not cover this, then it's very likely this is what Azem was off doing during Zodiark and Hydaelyn and the Sundering. If this also leads to what was originally causing the weakening of the Aether as well, then we have an underlying link for things. Especially considering how the FSH quest for the Studium pointed out how the fish ended up going all over the place into regions they're not supposed to be with Zodiark's death, the aethercurrents went out of whack with his departure.