The questions I want EW to answer the most: WHY and HOW was the world sundered?

[Cleretic]

I see what you're saying, but issue at hand is the Ascians have claimed to have been tempered by Zodiark. So if Zodiark can temper them and they have the echo, it's possible that Hydaelyn has tempered the WOL. Even if it isn't to control them and allows them to think freely but at the same time protect them from other primals. Hopefully this is fully clarified in Endwalker.

Again; it's not possible that she has. Even if you dismiss that Ifrit directly clarified this exact point back in ARR, you then need to acknowledge 'why would the Ascians not use this information against us', because they would also know exactly that, and Emet-Selch and Elidibus had every reason to crack it out if it were true, so we can reason that it's not. And even if you dismiss that, you then need to acknowledge that the Scions have exactly the same information as we do, and still never bring it up, almost as if it's not a conclusion that reasonably educated and trustworthy people in-universe would think is credible.

And if you dismiss THAT... who do you want to hear from to believe this? Because I feel like you wouldn't believe Hydaelyn herself, and yet that's basically the only higher authority left to hear from on this.

But, again: there's nothing saying she can't temper us, just that she hasn't.