The Oral Gospel Tradition,
James D. G. Dunn, Eerdmans, 2013
Chapter 7, "John's Gospel and the Oral Gospel Tradition", page 195
In the last of a short series of quotes from James Dunn's important book about the orality of the gospels, he makes sure that we understand that the difference between John and Synoptics has significant effect:
The most obvious way to explain and understand the distinctiveness of John's portrayal of Jesus is that John knew well the tradition that he shared with the Synoptics, and that he wove his much more refined fabric from the same stuff as the Synoptics - the product and expression of many years of reflection on the significance of what Jesus had taught and done and on the significance of the revelation he had brought and constituted in his life and ministry.
It is the same story, really. Different in viewpoint and emphasis, maybe. But essentially the same. And still reliable and G-d-inspired. Let's let Dunn finish:
While we should not understate the distinctiveness of John's Gospel, given the many echoes and parallels in John neither should we exaggerate the difference. John in his own way was telling the same story as the other Evangelists. That he chose to do so by elaborating that story in his own way should be acknowledged and properly appreciated. John's Gospel should be valued for what it is, not for what it is not.