Same source etc, but different religions ?

[Wyrd of Gawd]

Jesus wasn't a Christian.

That's true. And neither was his brother James , who ran the Jerusalem church after he died. The Judeao-Christians gradually died out and Christianity became a blend of Greek ideas (the Trinity) with stuff borrowed from all over. Stuff from the Essenes. Virgin birth etc. Paul had to make Jesus Divine so they added the Resurrection. They failed to sell it to the Jews.

Paul created the Jesus character as a way to subvert The Way cult. Paul laid out the basis for the Christian doctrine, which was the resurrection of Jesus. Years later his disciples who the back story which explained why Jesus was worthy of being worshiped.

An alternate theory is that a Roman wrote the story to mess with the Jews.

But based on the Bible narrative a strong case can be made that Paul made the whole thing up.