What's the point with that quite lackluster story in Endwalker?

[linayar]

I would've taken action in the past.

And in the process, lose everything that the WoL knew and cared about.

She openly stated she would let time repeat itself, thus withholding information from her fellow ancients. Newfound information that might stop the final days from ever happening.

Of course, that's one theory. What we instead received was an explanation we were forced to accept. She gambled on what some of us here would deem a lesser or immoral option.

Yes, in essence, she has hope on the WoL. It would've been terrible to answer that hope by fighting her for no benefit to the WoL.

I think they're referring to how Hydaelyn's backup plan would be for the people of Etheirys to flee elsewhere, which would lead to Meteion destroying the world and thereby the other reflections of Etheirys. Thancred, notably, was not entertaining the possibility of not fighting Meteion because he was worried about Ryne.

That said, if Hydaelyn is tapped out on power and the Warrior of Light can't defeat Meteion, I'm not really sure what else the backup plan could be. It's clear Hydaelyn would prefer that they can defeat Meteion, but she left an out for the people of the Source so that SOMETHING could survive in the event that result wasn't possible.

By fleeing, Meteion wouldn't have anything to do with the Source. If anything, that would've saved the shards, at least until Meteion finds them again. But that's why it's a last resort. It's meant to prolong their chance of survival.