Historical method is naturalistic for one simple reason - that there is no method of assessing the supernatural. It is quite noticeable that historians are prepared to discuss the bare bones of the life of Jesus, but not the resurrection nor other miracles.
But I think the mythers have gone to the opposite extreme, and suggest that it's all legendary. Well, it might be, but a historic figure who is a Jewish preacher, sans miracles, is a parsimonious explanation. Also, some of the mythicist explanations are really florid.