The other god-slaying divine abilities in the reward list are not better either. So Legion-7 is the best that he can get for a single divine ability that targets gods. The Supreme Alliance needs a combination of divine abilities or different classes to target gods.
The best case he saw was the divine ability that can be used to curse gods. The divine ability can curse any being so it is not specially designed to harm gods.
The main requirement for the divine ability to be effective is to use something that belongs to the target as a channel for the curse. It just so happens that believers belong to a god and can be used to great effect to curse their god. The cursed god will weaken and be unable to create divine energy for some time.
