So Mrs Mark comes home, and says, "Mark, you're still staring at that blank sheet of papyrus same as two hours ago." Mr Mark says, "True, my dear. I need to write a biography of Jesus, but none of us knows anything about him on earth." "Why don't you get out the scriptures, and make a list of things that you could say were messianic prophecies? Then all you have to do is write a story about Jesus doing one of those, and maybe sort out the order a bit, until you think you've got enough." "My dear, you're a genius!" And he gets out his Tanakh scrolls and starts making the list."It is far more consistent with a significantly embellished biography of a real person than a completely mythical person. A completely mythical person wouldn't require such convoluted attempts to make him meet the messianic expectations of prophecy such as getting the lower-class Jesus of Nazareth to be born in Bethlehem of the lineage of King David.
,
Which is simply another way of saying that Mark can be mapped onto passages in the Tanakh, perhaps some ideas of Paul, and the trial of Jesus son of Ananus/Ananias in Josephus, all but completely. And ten years later the author of Matthew, disagreeing with aspects of the Mark's notion of Jesus (such as being born of ordinary Jewish parents and not being divine till his baptism and denying that descent from David is important for an Anointed One, and despairing too much on the cross), but having minimal biographical information of his own, but maybe having a copy of Q he likes, rewrites the story, giving Joseph a fictional genealogy back to David, and angelic messengers to Mary and a flight into Egypt (Exodus 4:19 for the set-up, Hosea 11.1 for the knockdown) ─ and so on.
So while there may have been an historical Jesus (and if there was, his followers, at least by the time of Mark knew almost nothing about him), we can go a long way to accounting for Paul and Mark without one. And once we have Mark and maybe Q we can equally account for the other gospels ─ and why the NT has five incompatible versions of Jesus.