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

[Turtledeluxe]

Yoshi-P already answered that question in the link the poster provided. In short, the sundering required utilizing her power to its utmost limits. The monumental effort required made the technique something unwieldy to say the least - virtually uncontrollable, and so she was unsure if her attempt to give Emet-Selch an out would actually work. It was also partially up to the man himself; he needed to recognize what was happening, spot the "flaw" in the sundering, and take action to preserve himself.

How was she unsure when she knows his future is at the bottom of the sea playing games with their city? We told her all this. Emet existing in his og form post sundering absolutely requires that he survive the sundering. If it's all one timeline, if Venat is fully informed, then it isn't a gamble. It's a choice.

I also forgot to address Graha-- yes he time traveled and unlike us, he stayed there for a long time. It's unclear what would have occurred on the first without his visit.