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

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.

Change was inevitable for Amaurotine society. Azem's departure from the Convocation was unprecedented and challenged the foundation of their leadership. The act was so egregious that the Convocation refused to fill Azem's seat, refused to commemorate them, and henceforth referred to them as 'the defector' (Hythlodaeus, Lv.80, Etched in the Stars). We also now know that society's views were also changing in parallel to this challenge. People lost faith in the Convocation's leadership. They began to question whether Amaurot could afford to be so reliant on Creation magic, seeing how spectacularly it had backfired on them (EE(3), p.11). Times were changing, and the Convocation failed to acknowledge this and change with it. A coup would be inevitable under such an impasse, although under any other leadership it would have likely have ended in a complete massacre in the Convocation's favour.

The final potential branch point is an unexpected one. Emet, Lahabrea, and Elidibus had to be unsundered. Emet Selch needed to be present in the lifestream with his memories intact to create a way forward in Ultima Thule. Lahabrea and Elidibus also needed to have their memories be intact within the lifestream for the resolution of Pandaemonium in the present. Deviating from this would have resulted in failure of the corresponding plotline and the destruction of humanity.

When you look at it from this standpoint, it becomes obvious that you can't just meta-game your way through the various branches. A lot of seemingly 'sensible' solutions to try to deliberately alter the future would have resulted in tragedy. This is likely also why Alexander didn't meddle in the timelines, despite having the power to do so. 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.