I completely agree with your observations. I'd add, however, that Jesus' message was not that radical and different -- even in context of Levant during Jesus' times, non-dual understanding of reality had to have been known.

It was certainly known in times of Abraham and Melchizedek, and later dug up from under the ballast of polytheism in Moses' times. Jesus was another "reformer" who attempted to bring Judaism back from legalism to its non-dual roots. Alas.

Well, and non-dual understanding was never lost in the East, though, judging by Siddhartha Gautama's work at restoring Vedic Hinduism (he was a Hindu after all), Vedic tradition succumbed to shamanic trance practices in the same way Judaism succumbed to (de facto henotheistic) legalism.

https://senderspike.medium.com/from-animism-to-non-duality-c12eb05fb439

Sadly, both, Buddhism and Christianity, are nowadays infested with the same original problems that plagued their predecessors -- mistaking meditative absorption for enlightenment and considering adherence to dogmatic legalism as a way to salvation respectively.

And yes, the root cause is (at least in the case of Christianity) that neither apostles, and certainly not Paul, had a clue what was Jesus actually talking about. And that was already obvious during 1st-2nd century CE:

https://senderspike.medium.com/why-jesus-never-had-actual-followers-21c901810e1a

https://senderspike.medium.com/against-heresies-and-irenaeus-fdecb4272025