"If we are created in God's image and we are potentially good but then choose evil, perhaps we were evil all along."

Hum, that view could be problematic, too.
But maybe it doesnt matter, because we can't go back and choose the un-evil, whatever that is. That does not mean we were evil all along, it could have been just at that point in time; before we couldnt have been choosing that evil, nor after.

"God" and "the devil" could not be at war within us, even the Christian religion does not say that. I dont know much about Dualism, other than it says something like that, but is ultimatley flawed.