The NT text as we have it is very sound. 18 of the 27 NT books were universally accepted from the beginning, and most of the others had early and widespread support. We shouldn’t let the few books in dispute muddy the waters too much.
That is how I understand it too.
Among the most important evidence against the Resurrection being a late add on myth is: The Pre-Pauline Creed (30-35 AD). It is very difficult to explain away the Resurrection as a late addition. It is very difficult to explain away Paul’s conversion, and the apostles acceptance of him as an equal.
Also, the claim that Jesus is a composite of other figures does not hold water. We know who the other Messiah figures were at this time. There is no indication that Jesus is a composite of them.
If we are as scrupulous with the evidence here as we are with biology, we would reject many of these theories as obviously false. Something happened early on to form a new religion in 1st century Palestine, even though we do not expect such a thing to happen. There are no examples of messiah movements lasting beyond the death of their leader at this time, while still maintaining their executed leader was in fact the messiah. There are no other examples of messiah movements at this time claiming the messiah bodily rose from the dead, and then altering the traditions so radically, after he was dead.
Something happened back then. I, of course, think it was the Resurrection. You can disagree, fine. Disagreement is certainly rational because we know that people do not rise from the dead, right?
I’ve yet to see a more parsimonious explanation for all this data. There is no good explanation of why or how this Resurrection story arises in 30-35 AD in this cultural context. It clearly, however, did arise almost immediately after Jesus died, and is the core believe around which Christianity is founded and grows. There would not be the four Gospels if not for the Pre-Pauline Creed.
I’ll point out too that Jesus makes a very similar claim about his Resurrection in totally different language (Sign of Jonah).
39 But he replied to them, “An evil and adulterous generation craves a sign. Yet no sign will be given to it except the sign of the prophet Jonah, 40 because just as Jonah was in the stomach of the sea creature for three days and three nights,[b] so the Son of Man will be in the heart of the earth for three days and three nights.41 The men of Nineveh will stand up at the judgment and condemn the people living today,[c] because they repented at the preaching of Jonah. But look—something greater than Jonah is here! 42 The queen of the south will stand up and condemn the people living today,[d] because she came from so far away[e] to hear the wisdom of Solomon. But look! Something greater than Solomon is here!”
If this is a late addition, it does not fit expectations. Rather than using language consistent with the now well developed creeds in a Gentile church, we see Jesus speaking inseparable from his Jewish context. The contrast between Paul’s and Jesus’ language is very important here. At the time Matthew and Luke are written, Paul does have a very large influence on the Church. Here, however, we are seeing a minor story preserved in the oral tradition, in a time frame consistent with people who first heard it reporting it to the authors of Luke and Matthew.
Jesus uses the term “Son of Man” all the time and speaks of the “Kingdom of God”, but Paul does ever mention these terms. He calls Jesus “Christ” and "Son of God’, and emphasizes His salvific role. If a Jesus myth was being constructed at a late date, it would have supported Paul’s language and doctrine more directly, using his language. Once again, this sharp contrast in language adds strong textual support for these being more than fabricated stories. Remember, the Gospels are likely written long after Paul has made his mark on the Church, and also while people who were eye witnesses of Jesus’s ministry were alive and all over the place. What we see is two different voices arising that are unmistakably distinct, but also in harmony. The Gospels speak in a different voice than Paul, because Jesus had a different voice, and the oral tradition preserved that difference even as Paul was becoming very influential.
Once again, this strongly undercuts the notion that these were late additions, or part of a “Jesus Myth”. We have good reason to think think that Jesus actually taught something like this, in language approximating this. Which aligns very closely with the Pre-Pauline Creed.
Whether or not Jesus really rose from the dead, it appears everyone in the early Church really believed He did. This appears to be a “myth” without precedent.