From the beginning, Christians used the New Testament as their ONLY guide. Even the OT, while viewed as the word of God with valuable background information, was not in the same class as NT apostolic writings. Why? Simple. Christianity is a single event faith. Jesus rose from the dead. And that supersedes everything else.
The first book that would eventually become the New Testament would be one of the letters Paul wrote to one of the Christian congregations. That puts around 50 CE (1 Thessalonians was written around 51 CE). That's about 18 years after the death and resurrection of Jesus. Keep in mind that only the intended person/congregation who Paul was writing to had immediate access to Paul's letters. The Gospels were written around 68 - 110 CE. So that's a minimum of 35 years after the death and resurrection.
So we are not at 18 years after Jesus' resurrection that any scripture in the modern Bible was written. It was 35 years after Jesus' resurrection that the Gospels are written. That means for the first 18 years of Christianity only the Old Testament an Apocrypha were available. The "single event faith" that supersedes the Old Testament, written scripture, would simply be oral history - aka "story" or "gossip".
That is interesting as Paul writes Timothy in 2 Timothy chapter and tells him that "all scripture is inspired." The only scripture at that point was the Old Testament and Apocrypha. Paul continues that scripture is useful for "teaching, rebuking, correcting and training in righteousness". No mention of the word-of-mouth story of Jesus by Paul.
It is starting to seem to me that the entire New Testament is nothing more than some letters from Paul which are nothing more than him trying to steer the religion the way he wants it. Then a minimum of 35 years after Jesus' life, ministry, death, and resurrection someone decides it might be useful to write those events down. Paul even writes in 2 Timothy 2:8 "Remember Jesus Christ, raised from the dead, descended from David. This is my gospel..."
So, I guess I agree - the resurrection of Jesus is the single faith event of Christianity. It is just that it not Jesus' Gospel. It is Paul's.