What does the Indus Valley civilization have to do with monotheism? Are you saying they should have been monotheistic because they had a desert? Having a desert isn't a sufficient condition of monotheism. What the desert does is shape the conception of the monotheistic God when that simplification of the pantheon starts. And a desert becomes more of a factor when it's an overwhelming presence, as it is mainly in the Middle East where it stretches from Africa to China.

I don't know if monotheism is a distortion of monism. That would assume monotheism is based on an esoteric religious experience. The average monotheist's religious experience in the ancient world was more likely similar to that of average Christians and Muslims today: a feeling of being guided by intuition, destiny, etc. It wasn't likely a deep investigation of consciousness. I'd think Jewish monotheism formed for more political reasons than entheogenic ones. Jews got it from Persia or perhaps Egypt, and the captive Jewish leaders used that conception to lord it over the Israelites (in hindsight in the scriptures they developed).

I know there's some evidence that ancient Jews smoked weed, but it's too much of a coincidence that some Jews were captive in Babylon when the Persians conquered that region, and then you have have early post-exilic, Second Temple Judaism when monotheism starts and the canon is developed under Persian rule and guidance.

How is the core of monotheism similar in Judaism and Christianity? Judaism may be closer to Islam, but they'll differ in the angelology and demonology that make the religions more polytheistic.