speaking of which, I don't think I've made enough of the fact that, in a kind of terrible way, you could argue that G'raha and the folks from the timeline of the Eighth Calamity did in fact make the same choice as the Ancients.
minds capable of creating a machine that could traverse time and space and span the rift are minds capable of figuring out some other miraculous solution besides "we stay in the dead-end universe timeline and send our technomagical marvel back to save the lives of a specific group of people who have already died."
the distance between "a bunch of our friends gave up their lives to make this slim chance at salvation work, and we're willing to doom the rest of life in this timeline to correct what we perceive as the last, ultimate loss which doomed us" and "a bunch of our friends dedicated their lives to making this slim chance at salvation work, and we're willing to doom the rest of life in this timeline including ourselves to correct what we perceive as the last, ultimate loss which doomed us" is very, very small.
it's only the "including ourselves" that puts any distance between them at all
the Ancients decided that other life was worth sacrificing to right a grievous wrong (not in the initial sacrifice to summon Zodiark, but in the plan to bring their world back)
the Sons and the Ironworks workers and G'raha decided that all life was worth sacrificing to right a grievous wrong