What lore do you ignore?

[ZavosEsperian]

Even if you want to go the 'What if' route, you have an obligation to follow the restrictions placed by previous story telling.

To this point here, it would appear you are creating the restrictions pertaining to events related to Elpis and their consequences as the writers themselves leave anything involving how the timestream flows as open-ended, where the player/reader is the one free to interpret this however they like, be these converging or diverging timestreams:

Q: I don’t really understand why the Warrior of Light messing around in Elpis didn’t create any alternate timelines. Can you explain what happened?

A: First of all, we’ve left that part up to interpretation.

With that said, my personal interpretation is that the past and present were always the part of the same timeline. Although there was still a possibility for the timelines to diverge, the Warrior of Light was unwittingly acting in accordance with Venat’s plans, which unified the past and present. Another interpretation might be that Venat worked really hard behind the scenes to ensure that the timeline wouldn’t go awry.

Seeing how Argos took to us on our first meeting, I’d say that proves that the past and present were already unified. -Yoshi-P

Link to video with timestamp at（03:18:39)

Link to Forum Post

-Letter from the Producer LIVE Part LXVIII (03/03/2022)

Your interpretation appears to be more in-line with Yoshi-P's which is one of convergence. With that said, Yoshi-P and the writers are not dismissive of the idea of divergent timestreams, which would allow for more potential outcomes overall. So as far as 'What ifs' are concerned, under divergence they would be allowed to manifest should this be the approach taken. Generally, convergence would have to reconcile with various paradoxes (such as the bootstrap paradox and Ex Nihilo Paradox) in order to properly function unless we are still inside of the loop itself, however that is just an opinion in terms of my thoughts on converging timestreams.

For example, Emet makes it clear that was relatively easy for Amaurotines to identify deception. Not only did they have the power to read others' memories, but Venat gave a demonstration of how the land itself could serve as witness to a conversation that nobody else was privy to (Lv. 87, A Flower upon Your Return). We saw how quickly the Amaurotine trio on Elpis arrived at the secret behind our arrival once Venat started asking the right questions. Even revealing partial knowledge of an event effectively renders it public domain, which is quite dangerous.

We also know that any branch histories in which Hermes regains his memories prematurely are bad endings, as are any branches in which he does not join the Convocation or is ousted from it. According to Elidibus, Fandaniel was critical to the Amaurotine defense against the Final Days. As assayer of extant phenomenon, he was the first to identify that the transformations first took root at places where the celestial currents were weakest. He also dedicated himself to developing the countermeasure. This, in conjunction with Lahabrea's experiments on Archaeotania and the subsequent development of primal summoning, gave rise to Zodiark as the 'Will of the Star' (EE(3), p.10). Without his contributions, Amaurot would have perished then and there (Lv.86, Return to the Crystarium). Accidentally refreshing Hermes' memory would have been a relatively easy trap to fall into, given the nature of their society.

In the Lv. 86 quest Lives Apart, Hermes reveals that not only was Dynamis a relatively unstudied phenomenon, but that the rest of Amaurotine society had not sufficiently advanced their technological development to the point of creating space travel. This creates a catch-22. Hermes is the only person from that time period with the knowledge to create either an entelechy or a being capable of traversing space. But the very act of unlocking those memories would have rendered him uncooperative, resulting in a bad end. In effect, the only solution was to forestall the Final Days until society had developed the technology to mount a counteroffensive.

Everything bolded here subjected to the Catch 22 argument is a false argument. Per the MSQ quest Caging the Messenger, the only memories subjected to Kairos' memory alteration are those from the point Emet-Selch arrives to Elpis (and subsequently the WoL) up to the point where he is invoking Kairos. Kairos does not affect Hermes'/Fandaniel's prior knowledge/wisdom on Dynamis or space travel, as Meteion, along with her sisters, were all created prior to Emet-Selch's arrival.:

Transcript for Caging the Messenger

Transcript of events in question:
Kairos:
Memory reconfiguration system Kairos activated. Awaiting instruction.

Hermes:
Command: universal memory alteration. Target area: Ktisis Hyperboreia.

Starting point: arrival of Emet-Selch of the Convocation at Propylaion. End point: the present.

Erase the memories of all events, and replace with a vague recollection of the following:

I was here, preparing to demonstrate the functionality of Kairos to Emet-Selch and Hythlodaeus.

Meteion's shared consciousness became unstable. She and her sisters could not sustain their existence, and all dissipated with a burst.

The resultant shockwave accidentally triggered Kairos, which erased several days of memories from all present. Execute.
Kairos:
Command acknowledged. Initializing... Three processes remaining to execution

YT video with timestamp 8:25

-MSQ Caging the Messenger

With the timespan set, it would be impossible for him to wipe out his knowledge of both Dynamis and space travel unless all of these things occurred while Emet-Selch was present, which is contradicted by the fact Meteion has already been in existence prior to Emet-Selch's arrival. This based on her constitution paired with her ability to traverse space, and solidifies Hermes' knowledge of these fields prior to the events in Elpis. And given the timeframe Kairos affects, the claim memories/knowledge pertaining to those two fields was affected by the invocation of Kairos cannot be substantiated outside of someone inventing/headcanoning those effects.

As such, I am unable to view things from the standpoint you have presented them as they are contradictory to how the story portrays events. You have directly contradicted yourself with your argument via inventing/headcanoning information and presenting it as fact while maintaining a stance where people have an obligation to follow restrictions based on previous storytelling. In addition, to enforce rules on individuals for how people interpret events in the story while, at the same time, failing to abide by that selfsame standard is extremely hypocritical. I am relatively lax on many things, particularly if they involve sections of story the writers openly state to be able to be subjected to interpretation on behalf of the player, but I do not tolerate misrepresentation of events that are clearly depicted in ways that leave no room for any other interpretation.

The fact that we reached an ending where humanity survived at all was, in all likelihood, a lot of blind luck in dodging the multitude of bad ends along the way.

To peddle back a bit to the whole timestream thing, in a convergence scenario, this would be a correct interpretation of events. In the instance of Divergence, particularly if the idea of Infinite Alternate Timelines/Universes is invoked, this is just one of many permutations of the timestreams that, based on invoking infinity, would allow for this to happen, it just so happens we are in that timestream, which is also a bit of luck just like how it would work in terms of convergence.