The Pokey Finger of God

Does anyone have a comment or specific argument against Alvar Ellegard’s Jesus: One Hundred Years Before Christ? (Amazon) His argument is that Christianity developed from diasporaic Essene communities that had already developed a standing mythos about a “Teacher of Righteousness”, and that the later stories about a Jesus in Gallilee were much later accretions.

This guy is a linguist, not a theologian, but I find his arguments compelling. Can anyone point to relevant debate or contrary arguments?