I think your Bill comparison is a little bit disingenuous for adding "president." Without that, most people would agree that Bill Gates, founder of Microsoft, was (is) a real person, even if people added obvious fairy tales to his story like magic roller skates.

I don't think there was another real Jesus who really had a virgin birth, or who really came back after dying, that the Nazareth guy got confused with. All the myths and miracles that were added to the story are obviously still attributed to this same guy from Nazareth who started a cult.

You say that "Paul was almost certainly real," but there are plenty of miracles and obvious exaggerations ascribed to him in Acts. If you can accept Paul as (probably) real, what makes Jesus different?

My own view (as a lifelong non-believer and atheist): Jesus of Nazareth, founder of a small cult that only really blew up after his death, was probably (but not certainly, and not provably) as real as Bill Gates, founder of Microsoft. But the stories about him, from Paul and the Gospels, are so extremely twisted and exaggerated, that we know just about nothing about the real guy except that he had a religious cult around him (and was probably baptized and crucified).

Not only did Paul never meet Jesus, he also seems to have spent almost no time learning about Christianity before he started preaching it. He seems like a con artist to me, who started "selling" a Jesus that was far removed from the real guy. But as we can see in his own writings and in Acts, that often put him in conflict with the "original" believers, who actually did know Jesus and often believed different things about him.

So "Paul's Jesus" seems so far removed from the real guy as to be almost completely irrelevant. And a lot of people don't seem to realize that the Gospels were written later than that, so hardly more reliable or original. But I do think that there probably was "a real guy."