Not sure how time works in FFXIV since it keeps changing every story, but even with all of this knowledge of the future, the Sundering has to happen anyway in order for us to go back and alter events and tell Venat of the future so her path was set for her regardless.
The issue here is that it creates a time paradox that just raises more questions. We get told we can't change the past, yet we clearly do it by telling stuff to Venat. We either accept it an issue or buy in a time paradox that infinitely repeats itself.