The Jesus myth is almost verboten in NT scholarship. There are very few published historians who affirm it, the main one being Richard Carrier. He says the same thing. Jesus's historical existence is taken for granted by most NT scholars, although they admit it's only a question of probability, not of certainty. The question Carrier's Bayesian method raises is how high is that probability. As I recall, he thinks there's only one in three chances that Jesus lived as a historical person.

I side more with something Robert Price said on the matter. Even if Christianity is based on a legendary figure in history, the question is how closely the NT's representation of him reflects that source. If there's enough mythical and literary overlay, the historical existence of "Jesus" becomes irrelevant. Even his name, "Yeshua," is suspicious because of its too-convenient meaning (to rescue or to deliver).