I figure out a way to satisfy both faction, which is parallel timeline. We create a separate timeline where Hydaelyn didn't sunder the world. The question is, when should we interfere? There are two options:

1. After the summoning of Zodiark. From that cutscene we saw that Venat only sundered the world after she saw that everyone was too dependent to Zodiark (Emet-Selch even said they were tempered in a ShB dialog). So we came back to that time with a porxie, show that the tempering can be cured and just gave them as many porxies as they need. Then they will figure out a way to defeat Endsinger (maybe by creating another Meteion like being but showered with hope and positive emotions and send her to fight Endsinger).

2. Before the Final Days actually came. We know where Endsinger is because Venat gave us the location. So why don't we go back to the past and fought her there before she started the original Final Days. We can also do it in option 1 but I think it's better if the ancients themselves defeat Endsinger.

Which one is better? While option 2 seems better, I can argue that option 1 is actually better. In option 1, the ancients will have experienced depression and overcome it. If this happens again they know how to fight it. In option 2, life would continue the way it was and it's just a matter of time before another Hermes does the same experiment and cause the Final Days. Or it will end like the third part of the final dungeon where they will create a god and ask it to kill them all because life has become too boring and stagnant.