I am an atheist and I care about the truth. It is very very difficult to get a historical Jesus to fit the data. We have to assume so many people acted in unexpected ways in a precise sequence of events.

You are right however sometimes mythology does have roots in the truth. Judaism already had a story about a man leading a revolt, dying in combat, and his young follower taking over. The Macabees. James the Just would have been able to exploit that story in creating his mythical brother.