Certainly, you'd have to explain the polytheistic mythologies that persist despite entheogens, so you'd have to posit some complications or other factors, such as geography, climate, and history.

A problem I see with looking to a common ancestor is that messages are garbled over time, especially in the ancient world, so why should we expect the core of monotheism to have remained intact as it was passed along through history?

Why not just say that religion evolves from animism to polytheism to henotheism or monolatry to monotheism to pantheism? It's a question of simplification of the original childlike, mythopoeic vision of universal sacredness which is ironically recaptured finally by late-modern atheistic pantheism. In between there are stages of reconciliation and progressive disenchantment as civilizations mature and pass on knowledge and skills to later generations.