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

[dapperfaffer]

Her and her followers literally say in Anamnesis that Zodiark isn’t a permanent solution. Sooo…unless she was lying, in which case that makes her look even more evil than she actually is lol.

And when you beat genocidaelyn for her trial Yshtola says that when she sundered the source into the 14, decreasing the amount of aether they carry in their bodies, allowing them to overcome despair, to be able to face Meteion genocidaelyn responds:

"It is as you say. It was the trial I subjected mankind to that has lead to untold bloodshed and suffering. There was no justice or kindness in the tragedy I caused."
"When confronted with the Almighty Zodiark, my only recourse was to rend him and the world asunder, that his power be diminished for a time."
"And so it came to pass. Now you, my chosen, have surpassed my expectations. Surpassed me."
"I entrust the fate of the universe ... unto you."

And then proceeds to prattle on about the Mothercrystal. The later explanation in this cutscene actually mcguffins everything since it means that genocidaelyn created a time loop paradox.