The key on the Baptism is it's relationship to the Source of Authority parable. The entire purpose of Jesus responding when asked where his authority comes from is to show that his authority derives from John's baptism of him, the source that brought the spirit to descend upon him. To deny Jesus' authority would be to deny John's.
In the Marcionite gospel this is nonsense. But there it stands (AM 4.38), an example of editorial fatigue, or perhaps the author didn't recognize that the passage's message was dependent upon John's baptism of Jesus.
Klinghardt in my view has it backwards, because he doesn't recognize the role sectarianism had in developing the gospels. So instead of tendentious motivations he is looking for a general Catholic evolutionary line of development. My view is that the proliferation of gospels is the result of intense sectarian competition in the mid-2nd century and that Catholicism developed later on through the synthesis of some of these sects (the triumph of ecclesiastical politics), and is only present in the later layers of the gospels.
As for order, my view is we started with a synoptic prototype, which developed as something of a snowball. Somebody gave it some order, and I think it circulated in cenobitic Christian (or pre-Christian if you will) communities, perhaps as a religious play, but not yet as scripture. Anyway through the miracle of time and transmission, it took on some localized forms, not too different from other uncontrolled texts. Two of these forms became the base documents for the synoptic gospels. Mark alone used both of these forms, which in my view accounts for some of his at times awkward Greek, the messed up attributions such as Malachi 3:1 to Isaiah. Marcion used a version I call "L" (for Lukan path) and Matthew a version I call "M" (for Matthew path) as their base documents. Matthew also used the Marcionite gospel and I think referenced also the Antithesis in his sermon on the Mount. Luke is a revision of the Marcionite gospel, and borrowed passages from Matthew and Mark as well as some elements from what appears to be the traditions we find associated with the so-called Ebionite gospel or possible the Gospel of the Hebrews. John appears to me to have originally been a free hand derivation built off the Marcionite and early form of Matthew. A second edition of John was written to harmonize more with the synoptic accounts, and it was at this time some Markan language was picked up. Each of these came from different sects, with different theologies. If you notice I do not exactly place Mark, except before Luke and the 2nd version of John. I also do not address the order of later smaller revisions (e.g., Thomas layer in John). But using the principle of only writing a gospel if you cannot use the exiting ones, I come up with this dependency list:
Gospel[]b] | dependencies | key points |
Marcionite | "L" | Marcionite sect, Paul is patron saint, anti-creator |
Matthew | "M", Marcionite | almost Ebionite, Peter might be patron saint, anti-Marcionite |
Mark | "M", "L" | uncertain sect, possibly Andrew is patron saint |
John 1st Ed | Marcionite, Matthew | almost Cainite, possibly Modalist. John is patron saint, anti-creator, anti-Matthew |
Luke | | Marcionite, Matthew, Mark, Ebionite/Hebrews?Adoptionist leanings, almost Catholic |
John 2nd Ed | John 1st Ed, Mark, other synoptic(s) | Catholic, relationship to Luke uncertain |
Mark can be anywhere in the order from the time of the Marcionite gospel until Luke is written to replace the Marcionite. Worth noticing, Q is missing, because it didn't exist and is not needed to explain the order. No phantom 1st century communities need exist for this model. It should be noted that Catholic for Luke and John only meant that Jesus' resurrection was physical.
In my view all of these were composed in a rather tight window, from around 140 AD to 200 AD, most of the activity in the 145 AD to 175 AD window. Evangelical competition drove the proliferation. Ecclesiastical consolidation ended the process - making money to run the growing organization outweighed ideological/theological zeal.