For example, “the Didache is primarily a witness to the post-redactional history of the synoptic tradition.” (The Reception of the New Testament in the Apostolic Fathers. 2 and the double tradition material contained in Matt. The case for Ignatius’ use of the Fourth Gospel is more marginal …
p.127) and that ” it appears unlikely that Ignatius used either Mark’s or Luke’s gospel, the parallel between Ign. One must, therefore, be content with the conclusion that a strong case can be mounted for Ignatius’ knowledge of four Pauline epistles and the Gospel of Matthew… p.185-6) While the contributors of the committee were reluctant to declare the Apostolic Fathers’ knowledge of the Gospels, and I perfectly agree with them, they did not jump to the conclusion that the Gospels were written later.
Vinzent simply did not go through the massive amount of evidence on the development of Q before he discarded it.
When I saw his survey of the arguments for Q and 2SH just from the introductory chapters in Kloppenborg’s Excavating Q , I was certainly unimpressed.
Vinzent proposed that Marcion of Sinope was the founder of the Gospel genre known to us in the Synoptic literature and therefore the terminus post quem of the Synoptics should be pushed as late as the time of Marcion (around 144 CE).