I suppose you're right about the context of atheist.
So, is there a way to get your followers to go far enough beyond believing to grant you power? Could organized worship or sacrifice qualify, or would they just have to promote your spheres enough that you (and presumably anyone sharing your spheres) were able to draw strength from the incident?
In this game, worshipers don't grant power so its not a worry.
Tough question here. My flat rule is that the 'belief' of worshippers only increases their loyalty and their likelihood of success at certain tasks (religious fervour).
However, if sacrifice and organised worship play a significant role in their worship, it is possible that these acts may bind their loyalty/belief further, giving you a bonus to their belief.
As for acts relating to your sphere... Well, this can work actually, but I'd say it depends on location and scale. Say your worshippers wreck the dams/river banks in a location, flooding a plain. Local bonus to Water & Destruction. No gain in acts, but more influence for Water/Destruction gods there and divine Acts or commands will be cheaper/easier.
Say a cabal of insane wizards melts the ice caps,
major bonus to Water and Destruction that turn as the planet floods. Easily 4/5 bonus acts' worth, divided amongst all the gods with those spheres (in the event of odd numbers, who gets what is decided by random chance).
In summary: If your worshippers perform acts that empower a certain sphere, gods relating to that sphere may get bonuses. Ritual sacrifice and organised worship will not empower
you, but they may promote devotion or have economic/political benefits (and penalties!) for your worshippers, which may help them perform tasks that you command of them.
Edit: Also, phlegm beasts? Dear gods, man, what have you created?!