So a few things are bothering me about this;
-Calamities happen as the shard is being rejoined with its aether being shoved back into the source
-Zodiark is said to only need 1 more rejoining/calamity to have enough power to free itself from its bindings
-The Exarch is from a future where the 8th Calamity/rejoining happened
-This future is far ahead of when the 8th calamity took place
-Emet-Selch said they were going to use the existing life on the source to bring back the Amourtines that sacrificed themselves to save their world.

So i have to ask ;
  1. Why does The Exarch have no recollection of Zodiark who should have been freed?
  2. Why was life allowed to carry on? (since Ironworks were very much still going)
  3. Are the Acians being outright lied to by Zodiark? they are tempered after all
  4. Has Zodiark gained a will of its own beyond it's original purpose?
  5. Are more rejoinings actually needed beyond the 8th?