Endwalker's message (spoilers!)

[Iscah]

A. If she lost her memories to become a tragic hero, she never would’ve become hydaelyn

I disagree on that front. Prior to this game releasing, we had absolutely no issue with the concept that Venat's team had simply looked at the Convocation's creation of Zodiark, concluded that there was some critical flaw in the design and created Hydaelyn to fix it.

I think the plot would have been neater if Venat had lost her memory along with the others and later created Hydaelyn for her own reasons, not because the mysterious time-traveller said she would. Given the focus on "regaining lost memories upon death and return to the aetherial sea", she likely would have remembered the truth upon becoming Hydaelyn, so the conclusion in the present day would play out the same.