Wait... what?

The 1st Shard has not been Flooded as of 4.3. True, 4.4 may show us otherwise, but until then, everyone (the WoD, Hydaelyn) knew the Flood of Light would be stopped before it happened.

The Rejoining needs to be prevented if all life living on the shards is to continue to exist. Whenever a Rejoining happens, all life on that shard is turned into aether and goes back into the aetherial sea.

All the Ascians (except Elidibus) have been pretty transparent that they do not want a balance between Hydaelyn and Zodiark to happen. What they want is for Zodiark to be restored and Hydaelyn to be destroyed. By default that means all life on the shards will cease to exist. And I'm almost positive that Hydaelyn is the aspect of order and Zodiark is the aspect of chaos...