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

[Lauront]

Yeah I don't consider a picture from a random youtube channel to be canon unless you can link me to the story on the actual SE site where it says this.

Emet-Selch said himself this:

(Im not sure how to link pictures here in case this isnt showing up:
https://www.dropbox.com/s/vw971lybm7...t%204.jpg?dl=0

It doesn't matter if you consider it to be canon or not. It is depicted from a crossover event in that game, which Ishikawa herself authored.

Your screenshot doesn't support what you're saying, either. He just says 'appearance' there. I don't have the EN version to hand, so I am going to quote from the FR one:

Emet-Selch : En tant que garde-fou de Zordiarche, Hydaelyn était dotée de capacités tout bonnement extraordinaires.
= “As Zodiark’s safeguard, Hydaelyn was endowed with simply extraordinary capabilities.”

[14:00] Emet-Selch : Des attaques qui, en plus de toucher l'enveloppe matérielle de l'adversaire, tranchaient jusqu'à son essence même... C'était du jamais vu.
= “Attacks that, in addition to touching the material envelope (body) of the opponent, cut to its very essence… It was never seen before.”

[14:00] Emet-Selch : Supposons que vous subissiez un tel assaut. Vous seriez alors scindée en deux personnes distinctes.
= “Suppose you were subject to such an assault. You would then be divided into two separate persons.”

[14:00] Emet-Selch : Vos incarnations se ressembleraient comme deux gouttes d'eau, mais chacune ne posséderait plus que la moitié de ce qui vous constitue, que ce soit votre force, votre intelligence, ou votre âme.
= “Your incarnations would be like two drops of water, but each one would possess only half of what constitutes you, whether it be your strength, your intelligence, or your soul.”

[14:00] Emet-Selch : C'est ce qui est arrivé à Zordiarche, et à cette planète tout entière.
= “That is what happened to Zodiark, and this entire planet.”

The EN version is the same, and someone else can supply the remaining screenshots for it.