So all those Lunar Primals are all in one place and off we go to kill them in a 4 man dungeon? I've said in the past that these things are a means to an end and now I'm sure of it. These primals born from the towers are just batteries to be killed by us to release entire regions worth of aether in one location. They are important only in that they need to die in one place so Fandaniel can have all that power to enact his real plan. 6.0 trailer has Garlemald in ruins with towers seemingly made from charnel and this 5.5 trailer has Garlean soldiers acting like zombies. He is draining as much life as possible, that's his scheme.
Acting a lot like his mirror Hashmal did in FF Tactics. Plunge a realm into war and use the death and destruction to summon an ancient being of chaos to bring about the end of the world? Sounds familiar. He even said as much earlier on the the story. Just wait until he kills himself at or near the end of 6.0 to complete the ritual.