... for a start, Paul's letters and the gospels are in any case describing Jesus as a fictional character of past legend. Eg, the only way people can now try to make a real historical Jesus from that biblical writing is to discard all the numerous miracles, visions, voices from god etc. ... but that's inventing a new modern-day Jesus who was never the legendary figure who Paul, Mark, Mathew, Luke and John had once written about.
No they are most certainly not! They are describing Jesus as a person of their own time who really existed as a physical human being in the recent past.
Well first of all, Paul and the gospel writers were not actually writing about Jesus from anything they personally knew, because they all thought Jesus was dead by the time they saw him in visions etc. So Paul and the rest were actually writing about what they believed as a “legend” of an earlier messiah (Jesus) who none of them actually ever knew.
But directly on the point above - Paul and the gospel writers most certainly were writing about a fictional figure (whether they realised it or not), because the messiah who they described was an impossible supernatural figure. The only reason that Paul (for example) may have thought Jesus was a real individual was because he believed what others had told him about Jesus (he only ever knew Jesus as a risen vision of the supernatural), but the problem with that is … Paul clearly could not tell fact from fiction, and neither could any of the gospel authors.
No, it is attempting to discern if there is a probable reality under the layer of evidently mythical accretions. We have been through this with King Midas of Lydia. The sources make him a mythical figure with a golden touch. He wasn't. Scholars "invented a new modern-day Midas" without a golden touch - and his tomb has been found. He really existed. As to the golden touch .. it was in Lydia in his day that gold coins were first used; clearly the source of the myth.
Have we also found the tomb of Jesus, then? What physical evidence has been found to confirm Jesus was a real figure?
The problem with trying to discard all the constant miracles, all the visions, and transportation to heaven etc. etc., is that when all that is removed you are left with a Jesus messiah who fulfils none of the expectations of a Son of God, and who would not have been worth anyone of the time ever writing about. And that’s apart from the fact that all of those authors (whoever they actually were) were only ever writing about a messiah none of them had ever met, seen or heard, who was believed to be a figure of the past, and where their knowledge of him came only from their belief in stories that other unknown people had once told about a legendary messiah who was now dead!
Because they were writing about what they believed was a real figure, and telling exaggerated stories about him.
They may well have believed the stories about Jesus. They would certainly have believed that miracles and visions of god, angels, demons etc., occurred regularly every day. In fact at that time people did not merely “believe” in miracles, they were completely certain that miracles were an unquestioned fact. So when they heard stories of a miraculous messiah of the past, they could easily accept it as unquestioned fact.
But now, in the 21st century, most people know that all those miracles and visions etc are fiction (“mythical” if you prefer that word).
It’s not just an "exaggeration" to believe that Jesus had once walked on water, raised the dead, and appeared to 500 people at once after he was dead for three days and floating away to heaven etc. That’s not merely “exaggeration”, that’s myth! And remember that it was also a legendary “myth” … none of them knew anything about Jesus except as a matter of earlier legend.
What appears to be happening with all those stories from the beliefs of Paul and the gospel authors, is that they were following the practices revealed from 200 years earlier in the Dead Seas Scrolls, and deliberately interpreting their visions and religious imaginings as real events being communicated to them direct from god.