While we're on the subject of Goddesses who mean well, the actual true nature of the Sea of Chaos that consumed FFXIII-dom wasn't simply "the dead souls of humanity."
It was the dead souls of all the Yuls who died throughout history. As in, there were that many, and Caius knew all of them. Etro reincarnated the same person so many times their souls combined into a world-devouring horror.
Kind of a shame it got relegated to a sub-episode after all that buildup.
So yeah. If Hydaelyn is pulling anything like that, we need to stop her, even if she means well. Ideally with a non-lethal option. At any rate, I'm guessing that restoring "equilibrium" means finding a way to bring back Zodiark without killing Hydaelyn in return (and not simply trading light for darkness). End goal being that they oppose each other for eternity and leave us out of it.