I still operate under the idea that the Ascians are the Allaghans that did something that ripped there existance and world apart. Kind of like a phase shift. A veil has dropped across Eorzea after this event. Those Ascians were stripped of their corporal forms, and seek to return from the rift/other side of the veil to our world. Hence the Echo may let us see across this veil at times. But with the Ascians work of draining the aether... It might not be world lifestream but the aetheral magic of this veil being drained and weakened. Hence revealing, "the real world" as the Ascians know it. Hence why Crystal tower just reappeared one day after the Calamity. And the seal that was broken at Silvertear was the key needed to start weaking the veil.