Enjoyed the read. You provide a good overview of the 7th Umbral Era plot and how it fits in with the events of 10-15 years ago. I couldn't tell where you were serious and joking necessarily, but there were a couple of things that deviated from my observations of the game.
(1) I'm pretty sure the big flash of light when the great wyrm (Nidhogg?) attacked the Garlean dreadnought was the combined result of the explosion of its massive Ceruleum fuel supply and the death of the wyrm itself, which punched a massive hole in the aetherial fabric of the area, releasing Ifrit, Titan, etc. (2) I think the party we see is supposed to be in the present, whereas the vision is of the great battle set firmly in the past roughly 15 years ago and is likely a use of the Echo.