Now, the real questions begin since one line aside, we've got an easy 95% of the song as it's pretty clear: who's singing here?
In this case I think it's far less ambiguous than Answers ever was: the singer is either Hydaelyn-the-entity Herself, or one of the Seven Celestial Dragons. The first half of the song is, of course, a story. I suspect it's most directly the story of Shiva and her draconic lover, who I'd bet Gil on being Nidhogg at this point, and how they were eventually torn apart by differences in both their cultures (and a certain jealous king, I'd bet), and how Shiva specifically wanted this rift and fighting to stop, and tried to stop it, but in the end her actions were used to create an even bigger wedge. (Though you sure can turn the words around and apply it to a whole bunch of other people, too - "by treachery was broke, scattering her words to the wind", yeah, hi Nanamo.)
The fourth stanza is about the consequences - an age of blood, an age of people fighting for nothing, while those originally involved in the tragedy feel the pain forever. The last two, then, are actually the singer themselves - the person who watched this all unfold and just can't believe it's still going on, that the gyre of suffering the story opened still hasn't closed. Why are mortals so determined to destroy themselves? Why can't they see what was beautiful once and let it be? The singer never will know.
So yeah, I think this is all Hydaelyn (especially with that shot at the end of the video), but it'd make sense coming out of the mouths of one of the other Seven, too - maybe the one who isn't Nidhogg and has just watched this whole thing unfurl for aeons, or one from outside of Eorzea but is still tragically familiar with the whole story, perhaps the one who may have taken roost near Doma (as we know there were dragons near Doma).