I pointed out in my prior post that it was a combination of inaction and sabotage, not solely the latter alone. Giving the Ancients space to build up false hope and come to their own solutions is irrelevant when her reaction to the Convocation coming up with creative solutions is to wipe out everyone who survived the Final Days. None of the writing surrounding Venat is particularly consistent, granted, though one thing that is consistent is her decision to refuse to reveal the true cause behind the Final Days or express her concerns in full without deflection and deception.
If a character is well aware that a devastating event is going to wipe out the majority of the planet's population and they have the ability to either prevent it or at least forewarn the population that such is about to happen then they are a hero if they try to mitigate such things. If, instead, they allow for such an event to take place in the name of a Saw-esque style test of suffering then they are a villain.
It's as simple as that, really.
Let's imagine, for a moment, that Merlwyb learned that Leviathan was being summoned in secret and was due to unleash a tidal wave of devastating proportions upon the city of Limsa Lominsa. Merlwyb doesn't tell anyone what she knows and leaves the city abruptly.
The tidal wave strikes and destroys the city. The majority of the inhabitants are either dead or heavily wounded...and those present decide to do what is necessary in order to rebuild and survive.
Oh, but wait! They didn't react to the horrific even in the 'correct' way. So despite being understandably traumatised they also need to die...according to Merlwyb, who then kills the remaining survivors and replaces them with a completely different species bereft of their former culture, memories and remaining loved ones.
Scale that up to a global scale and you have...the Sundering. An act that, if aimed at the game's protagonists would never be deemed 'necessary' and an 'acceptable cost'. So there's really no obligation for anyone else to just shrug and go along with such consequences. It's what happened in the story due to how it was written, but that doesn't make it correct - especially for those of us who do not engage in the story as a self insert eager to have whatever benefits the Scions and a handful of other characters serve as the constant priority in the narrative.
Personally I'm interested in the world-building as a whole in a setting that I invest in as opposed to specific characters. If there's no consistency with the world-building and established morals, then I am going to be inclined to point it out especially in a game that is often obnoxiously preachy about 'dOiNg ThE rIgHt ThInG' elsewhere.