A lot of bodies in the thread like, "Sacrifices bad. Wanting the zenith of the Past, bad!" Ignoring that everything that could possibly be sacrificed was also robbed of agency and killed by the Sundering all the same.
"That Light split the world and every life upon it!"
From the tiniest termite to the broad, busty breast of her protégé, Venat sundered all Etheirysian life into 14 fragments reminiscent of their true selves, rapidly ending all life. And in this setting, the Lifestream is part of all life, and that got sundered too. Each shard has its own, and they're linked by some vaguely defined mechanism, but the Rejoinings and Soul mechanics previously demonstrated by the story's concept of Calamities/Soul Density show this to be the case.
Unfortunately, it has the unintended consequence of meaning that Venat also sundered most of the dead, too. And the unborn. And those awaiting rebirth. It turns out that in some, so far unexplained, maneuver that a few of the Ascians and those within Zodiark weren't sundered, somehow.
Then it's even told to us that the shards rely on the Source as a nucleus of sorts, so that the stakes rise higher, but this also intrinsically means that the shards are explicitly lesser to the Source, too. This opens up the sticky mess, that is a fact, that Hydaelyn's Sundering caused there to be Nucleus Lives and Orbital Lives, the Orbital Lives aren't even on the same dimensional plane. They can't even be made to come and combat Meteion, unless they are Ascian or unless they are Rejoined. Even the mechanism most important to our time conundrum and story came from an alternate Source, made by Nucleus Lives.
It's actually an incredibly complex vilification, and the real rub comes from essentially being told by the story to push that complexity out of your mind.
"Don't think too hard about all this, just go out and save the universe. It's for your own good."
"Her cannibalization of her own people was noble. They was no other way to live and win."
Survival is not intrinsically noble.
"Killing and eating my companion on the mountainside was noble. There was no other way for me to live."
It is actually a choice that debases her. Literally everyone who has said that the Ancients couldn't find a way and had no future are just echoing what Emet-selch said about the sundered.
So no, Hydaelyn wasn't a good girl all along. She was a survivor, willing to be morally unsound to live at the expense of everyone she ever knew.