Mythicism is just one of several categories of implausible claims that one will encounter in connection with Jesus. The Life of Antoninus Pius has a blog post about another one, that proposed by Francesco Carotta, who claims that Jesus was Caesar. Click through to read about it, and why no one ought to find it persuasive.
Carotta’s argument (found in his book Jesus Was Caesar: On the Julian Origin of Christianity: An Investigative Report) has many similarities of approach to that of Earl Doherty and other mythicists, showing the same disregard for counterevidence, the same willingness to allow one dubious interpretation of a detail to override evidence that is much clearer, and the same willingness to treat texts which make sense as narrations of legends and stories about a historical figure, as instead elaborate codes that mean something completely other than they appear to.
They differ in the details, but share a lot of things which fringe theories of this sort tend to have in common.