Sorry that I can't contribute to the philosophical discussion, I never could get my head around some of the concepts of theology.
I had a pedagogue at my academy -- I think he was from Samarkand -- he tried to explain some of the one god theories that keep popping up as analogous to a gem, where each god in a pantheon would represent only a facet of one whole divine being. Sorry, but the whole thought of all of these gods being separate, yet at the same time part of one being -- just makes my head spin.
Anyway, as for points of departure: my pedagogue said that this theory keeps popping up in the more mystical traditions of many hunter-gatherer and early agricultural nations. For example, a lot of the indigenous inhabitants of Avalon talk about a "Great Spirit" or "Great Mystery" - that's actually the translation of some of the Avalonian names for Jupiter, such as Waccantancus (Dakotian) and Gitsimanitus (Odzibvean).
I recall him talking about similar things happening in Antipodes and Australis, and even northeast Asia. I do specifically remember him mentioning the Druids in this lecture, although I don't remember what he said. Of course, the Druids were killed off in the early eighth century AUC, and didn't write anything down, so who knows what they really believed?
Wasn't there also some Egyptian pharaoh who tried to completely erase that pantheon and replace it with a single god?