Belief Empowers Deities, not quite the same thing. And thats just how it works for entities that have adopted those roles, like Odin or the Red King. The WG was on the ground floor of Creation, by WOJ (as a corollary to the WOJ that says Uriel was the Senior VP of Creation)
Point of order: that's not precisely what the WoJ says.
The presence of an Archangel, essentially an executive VP of Creation, probably had something to do with it.
People confuse the indefinite article for the definite one and then over-inflate the significance.
But that's not my point. I saw absolutely nothing in the text to indicate that the Odin we met was not the original Odin, and unless I'm forgetting something, nothing to indicate that the Reds weren't the original Mayan gods besides a moment of speculation from Harry "Unreliable-Narrator" Dresden. If there was textual support for that, please remind me of where it is.
So, given that we (currently) have no proof that Odin is any less real than TWG beyond Judaism, Christianity, and Islam being so very much more popular, that implies that the various creation myths are all true too, Susanoo and the backs of turtles right along with the Let There Be Light. So why must TWG be the only one who created the universe? I suppose it's possible that whichever religion produces the strongest deity at the moment could be the "true" story of creation at that time, but frankly that's a little distasteful, at least to me.
And, finally--we know that belief can create power wholesale, ala the Shroud of Turin. Does it really seem impossible to you that in the DV, thousands and millions and billions of people all believing in a deity couldn't make it come into existence?