It seems you have a deep knowledge of the times and are well read.

I believe you are on the right lines. You've read my latest article on Progressive Christianity, where it seems clear that the story of Jesus is that of a pagan mystery god, therefore based on the ideas of Paul and his Cosmic Christ rather than any historical Jesus. This suggests that the gospels were written by Paul's followers, most obviously in the case of Luke.

What's your source for “some Jews at the time were known to attend Mystery schools, in which virgin-born salvific godmen were a common motif?”