What lore do you ignore?

[Lyth]

...

No. We know that a divergent timeline did not occur. This is a thought experiment to determine if a divergent timeline was viable (i.e. one that does not result in the destruction of humanity).

I'm treating the timeline like a black box. Imagine a Radiant Historia style timeline map of the decision nodes. I don't know where all the individual decision nodes are or what choices were made at those nodes. I can't brute force a solution like Alexander can because I can't run tests of every possible outcome. All I can do is identify any constraints that would limit the 'form' of a viable solution. There may be additional constraints that I haven't identified that may restrict the range of viable solutions even further beyond what I've stated. These are entirely at the discretion of the writing team, should they ever elaborate further.

On the subject of space travel, Hermes cannot be directly used in any solution against Meteion. Hermes believes that the activation of Kairos was triggered by Meteion's shared consciousness becoming unstable, resulting in her destruction (Lv.87, Thou Must Live Die and Know). Venat elaborates further:

'As for Hermes... I think it unlikely he will create more entelechies. He poured much of himself into Meteion, and now that she and her sisters are gone - dissipated, in his mind - the grief must be unbearable. He will blame himself. He will believe that, had he never acknowledged his dissatisfaction with the world, then the Meteia would have never been born to suffer and die. The offer to join the Fourteen will be a welcome distraction, and one day hence, he will face the advent of the Final Days in the role of Fandaniel...' (Lv. 87, Caging the Messenger).

If you want Hermes to develop either space travel or entelechies further for you, you'd need to take him into your confidence and tell him what actually happened. We already know that leads to a bad end. As a result, any solutions which depend on Hermes developing these technologies further are non-viable. We also know that Hermes was miles ahead of his peers in his development in these fields, as I had established previously. As a result, you can't pin your bets on anyone else spontaneously developing those solutions in parallel. A means to forestall the Final Days is necessary. And we know the outcome of that.

Combined with the restrictions you've outlined it's hard to imagine any course of action that does not play directly into Meteion's hands, especially under the contextual constraints of time and the actions of others already in motion. It can be imagined, of course, but virtually all of the quest content, developer statements, and Encyclopaedia text supports that we're supposed to assume futility by the time the first two waves of sacrifices were made, the plan to sacrifice new life was decided, and civil war was at its climax.

I'm not saying the execution of the storytelling was clean, but I am saying that, when one knows where the developer's heads are at, rooting for one's counter-interpretation to pan out is - generally speaking - setting oneself up for disappointment.

Your final statement here is succinct and spot on. It's a bit like arguing with a DM/GM/storyteller in a pen and paper roleplaying game. They control the entire decision tree. We can propose whatever solutions that we like, but the downstream consequences of those decisions can render the proposed solutions non-viable.