I really hope it won't be that easy. All this build up to finally seeing the leader of the Kushan(which, by the way, they've been fighting the Kushan for ages it seems like) at his most powerful, just to have him get killed so easily, would be an enormous let down.
Also, I think that the only way Griffith could kill something like that easily would be to reveal himself as Femto, and he just looks too evil to be considered the Hawk of Light.
Likewise for most of his Apostles, how are they going to reveal their true forms without revealing themselves as demons? There's not one of them who looks like they haven't been born from Hell itself, wouldn't showing themselves reveal too much to Griffith's non-Apostle followers?