“The influence of Eusebius, and through him Constantine, on the traditional narratives of the development of Christianity is so great that one is tempted to say that they invented it. But that would be giving them far too much credit in my opinion and ignoring the typically diverse elements that precede all leaps and major changes.
In the case of Judaism splitting in Christianity, I see a number of developments necessary before we get to the 4th century.
1. First century anti-Herodian opposition movements trying to spread Yahwehism and combat Roman domination. Apostles dedicating their lives to this movement. The Christs (Anointed Ones) of Yahweh/Jesus
2. Supernatural (comic-book) stories of heroic traveling Apostles spreading the kingdom of God movement and working magic.
3. Mixture of prophetic and apostolic literature to create the gospel/son of God – Jesus Christ stories. A period of diverse gnosticism
4. The mixture of 2nd century gnosticisms in the Alexandrian cauldron of the 3rd century.
5. Eusebius and Constantine taking that Alexandrian potion and giving it a fairy-tale history in the early 4th century, which seems to have drastically increased its efficacy.
Until the application of C14 dating techniques to disprove or prove it, this is my best hypothesis.
Also, it seems as though the Gospel of Thomas was written around the same time as the other gospels; there are papyri fragments of it which are carbon dated to around 200 CE so the gospel itself must be older – probably around the early to mid second century.
And also, Lord Raglan’s Hero Scale (here), which Jesus scores pretty high on – around 19 out of 22. 22 being a complete fabrication and 0 obviously being real.