On the other hand, one of the reasons the gospels seem so "new and fresh" is that most of the contemporary literature we might have compared them with has disappeared. We know the Hellenistic world was awash with biographies of pagan holy men- but only one survives- Philostratus' Life of Appolonius of Tyana.
Similarly, none of the Pagan mystery cults with which Christianity is often compared has left any scriptures behind. All we have of them is their archaeology. Did Christianity borrow from Mithraism or the cult of Attis? We can only guess.