If I was writing the game then the main character of the introduction would be the real source of echo. During the "Bahamut"/Garlean fight he having the original power of echo (being able to see into the future as well) already knows the outcome of the fight and that there is nothing he or anyone else in the present can do to stop it. When Mor Dhona and Bahamut are destroyed and the Primals released it sets off some chain reaction that is both unstoppable and catastrophic.
We have the power of the echo because during the catastrophe that took place in Mor Dhona the introduction character sacrificed himself releasing it to all the player characters.
As our power of echo gets stronger we are eventually able to travel back to his time to give him the aid he and his party needs to defeat the dual threat of the invasion/dragons. After a tough struggle, we are eventually victorious and he acknowledges this to have been his plan from the moment he set eyes on the guildleve that day and had the initial vision.
(the guildleve was not the focus of the introduction it was only what they happened to be doing at the time of the attack, and what served as the trigger for the vision)
Now that we have helped avert the disaster in Mor Dhona we are free to enjoy the awesome zone it once was, and the character from the introduction who we finally learn the name of (Cid?!) becomes a recurring and prominent character in the rest of the FFXIV storyline.
The primals are still a threat but are "in check", and the beastmen can be a threat of their own (or maybe still allies, but probably threat first).
The Garlean invasion has been turned back, for now, they will likely attack again (maybe Ishgard), but it is time to turn the tables on the Empire and free Ala Mhigo!
