I'm not sure if it was mentioned in this thread at all, but I have a theory that Neal Van Darnus was presumably a Dragoon since he was so influenced by Bahamut (since Dragoons are vulnerable to the influence of Dragons). So in my opinion Bahamut has simply been controlling Darnus this whole time. This becomes much more apparent when he gets crazier and crazier as Dalamud got closer and closer.

So what I think is that all these events were of the doing of Bahamut, from bringing Dalamud closer to the killing of the primals to absorb their aether to the eventual killing of Neal Van Darnus and the absorption of his power as well to make himself powerful enough to break free from Dalamud.

But this may just be a stretch, who knows?