I have been thinking about summoning and the high concern on the aether cost and a question pops.
(A Ferne confirmation on this would be great).

So as Ferne stated when Beastmen tribes summon their primal and we defeated them same as the adventurers party in the CGI , we didn't defeat the real Primal we only put an end to the manifestation of them in our realm and they can be called again after the due fee of crystals/aether.

This leads to question. How did Bahamut's manifestation manage to stay in our realm after throwing a Megaflare if all hes got is the two meals of Aether from Garuda and Ifrit? which i assume they are small portions for an Elder Primal of Bahamut's caliber he must have run out of gas fast.(assuming he stays around after his rampage)