I think that you are all forgetting a couple of things. (And I'm going to address here those who profess to "Christianity" -- not others. I'm also not going to address the historicity of the Christian church, but the doctrines upon which it claims to have begun.)

First, not all of the New Testament was that which was taught by Yeshua of Nazareth. Perhaps more than half of what it is there was inserted later, by the leaders of the Christian church during the first centuries of the Church's existence. As just one example, study the person who was considered to be the "Apostle to the Apostles" -- Mary of Magdala. The early Church was full of dissent and came close to withering to death.

Secondly, Yeshua was most definitely not a "Christian" or a follower of "Christianity". He was a Jew -- circumsized and Temple-taught. He never claimed to be the "Messiah"; such statements appear to have been added after his death, as do the ones regarding "the fulfillment of the Scriptures."

Thirdly, if we assume that Yeshua did make such statements as "I will destroy the Temple and in three days rebuild it", "I have come to bring you a new covenant," and so on it should be clear that rather than fulfilling the Old Testament he was repudiating its teachings. Thus, to be a "Christian" you would have to drop the teachings of the OT as being no longer relevant to your religious beliefs and follow the teachings of the NT.

Fourthly, "Christ" comes from the Greek "Kristos" and means "The Anointed One." The man under discussion never used that word as a surname and most likely didn't know Greek (although that is under discussion). Yeshua's last name would most likely have been something like "bar Yoshef" (or, assuming a divine parentage, "bar El" or "bar Yehovah").