The Reasoning behind The Sundering? (*6.0 Endwalker Spoilers*)

[Absimiliard]

Venat had a necessary part to play in ensuring what she believed was the best possible outcome could come to pass, which did in fact require all those calamities and rejoinings. Whether she gave her all in attempting to stop them or not is moot; she knew going in what had to happen, and she had already resolved to do everything necessary to force her vision of the future (or rather the future told to her by the WoL) into coming to pass well before she sundered the world. She also knew ahead of time that she was going to see a lot more failures than successes.

What we have in Endwalker is called a stable time loop. The beginning and end points become largely irrelevant due to the fact that neither can occur without the other. Venat's decisions were always informed by knowledge of the future.