I was recently talking to some one who insists that everything is an allegory. Their argument with regard to the New Testament rests on one main argument. That is, that the dates of Christmas and Easter were formative in the myth creation regarding their relation to the Winter Solstice and Spring Equinox, respectively.
However, no matter how grand an argument one makes from this - there is always one fact that undermines the entire argument. That is - the dates of Christmas and Easter as celebrated in the Western rite churches today were not the dates that the New Testament makes reference to. For example, December 25th for Christmas is not even believed by those who chose the date to be a correct date for the birth of Jesus. It wasn't even used - as best we know - until AD 336. Quite a number of years after the New Testament Gospels. Furthermore, the Eastern Churches at the time - and the Copts to this day - celebrated Christmas on January 6th.
Regarding the date of Easter, we have a similar situation. Today the Eastern Orthodox Churches (myself included) celebrate Easter on a different date to the Western churches. (That is, the Easter date known in Australia, Great Britain, USA, etc).
Unlike the Western church date (which one can connect to the spring equinox as determined in 325) the Eastern churches pascha celerbations occurr in line with the Jewish traditions. That is, observing it on the 14th of Nisan - or, the first day of Passover.
So, as we can see, the argument is completely flawed at its core.