You forgot that there were people who witnessed Emet, Hyppo (forgot his name), Venat, and a so-called Azem's familiar entered the lv77 dungeon. People only knew that there was some problems with Kaitos that deleted memories of Emet, Hyppo and Hermes - the culprit himself. Even if Venat shows up and tells the truth, then people will just think that her memory got fumbled by the memory wiping device. Let's say Emet, Hyppo believed her and try to rally their people. It might make some noises, but the ultimate end is that people would just conclude these three having unreliable memories due to the incident. After all, it was 1 person who knew the truth, 2 people who had zero memory about what happened that just followed the flow vs the whole race who just wants to play god to perfect their star. And obviously, WoL could not stay there for too long to re-tell them the stories cuz the time-travel magic is running out right after the lv77 dungeon.
So Venat had two choices: try to change things, face a lot of opposition cuz no one trusts her, which could led to a future where she had zero mean to save the star, be it with the Ancient or with the new mankind. Or just make sure everything happening the same according to WoL's future, which she certainly believed would happen because WoL time-travelling to Elpis with her magic on him was the undeniable proof that that the sundering method was the right path that she needed to take. She needed Hermes in the 14th so that he would eventually contribute to the summoning of Hermes. She needed Emet to stay with deleted memory so that he would become the melancholic unsundered Ascian who built the Garlean Empire, which researched Black rose, which resulted in G'hara time travel to the First, which results in Elibidus getting absorbed by the tower who later provided information and a mean to travel to the past, then Fanadiel who opted for Zodiark's destruction, which led to WoL to the moon where he heard the word Elpis from the Watcher and received aid from the moon rabbits. And she needed to sunder the world so that everything above would happen, for a fighting chance against the threat nested in the edge of the universe.
Remember that she actually tried to reason with the Ancients, who was so absorbed with sacrificing to return to the blissful day instead of accepting suffering as part of their life and move on. And if you think they can "revive" the dead that easily, just look at what happened to the lamia girl who was the daughter that was killed and revived by Laskmi back in SB - an empty husk without soul. Zodiark is a band-aid for Final Days and a dead-end for the Ancient. A dead-end for the star vs a chance to fight back, Venat took the latter, and admitted there was no justice in her action.
And if you still think she just wanted to play Goddess, then what was the point of playing Goddess if your ultimate fate was the fuel for Ragnarok?