Young Jewish man runs into a Buddhist or at least Buddhist ideas in his twenties, spends a while learning about them, comes back to the temple in his thirties and starts telling people how great it would be if they were just nice to each other and maybe focus less on rules and hypocrisy. Gets killed by a Roman state that’s worried about uprisings and local Jewish leaders who don’t like different ideas. His followers tell stories about him in the following decades focusing on it being better to be poor, repressed, the Roman state feels threatened by a powerful underclass religion so they coopt it, make it the state religion, and shape it to be useful to empire. Ultimately it kind of contributes to the already crumbling empire.

All conjecture but reasonable enough.

If you start with the premise that Jesus was a real person but not divine, I think the real story would look a lot like that.