You messaged me directly rather than responding in the thread, but messaging back is failing, so I will respond here.
There is no theory involving deities that fits the models of the universe we have based on observable evidence, and there is no evidence in support of any theory involving deities.
For anything else we would say that this thing doesn't exist and leave it at that.
Agnosticism gets lost in the fallacy that since it's logically impossible to prove non-existence we must hold open the possibility of existence without evidence.
So I'm an atheist because it is the default state to be, it makes no statement requiring evidence, and it doesn't require fallacy.