Paul is well-attested, we have good reason to believe the authenticity of most of his letters, and while (per the less-reliable Acts) he never met Jesus in pers

Paul is well-attested, we have good reason to believe the authenticity of most of his letters, and while (per the less-reliable Acts) he never met Jesus in person, he clearly believed that Jesus existed. So the invention of Jesus would've had to have happened quite early. Most wholly-fabricated myths (e.g. the Arthurian legend) originate hundreds of years after the events are alleged to have occurred: the basic plot of Jesus's life is attested within two decades after his death. If we're choosing evidentiary standards that let us doubt Jesus's existence, there are a lot of other historical figures whose existence is cast into doubt.