A history of Christian origins that looks something like this, Stephan, might account for all that (and much else).
(A) RELATIVELY INDEPENDENT (with some possible interaction) IN THE PERIOD UP TO THE YEAR 70
- 1) Possibly Nazoreans, or possibly Jacob-(the-Just)-ians, or possibly Galilean Cynics, or possibly even revolutionaries, an Aramaic-speaking group (presumably), to be associated with the Mt//Lk synoptic sayings material, and to be located either in Jerusalem or in rural Syria/Galilee or both. (The most mysterious and difficult-to-pin-down group in Christian origins, which some don't even believe existed... and might not have...)
- 2) The Apostolic Movement, a Greek-speaking mystery-cultic association to be identified with the origins of the letters of Paul, and to be located in Antioch, Rome, Asia Minor (including Phrygia, Bithynia, Pontus, Cilicia, and Galatia--not just Ephesus), Greece, and Macedonia.
- 3) The Jewish Gnostics, Greek speakers to be associated with the earliest tractates of the Nag Hammadi Library and cognate material, centered in the intellectual capital of Alexandria but in correspondence with major urban centers such as Rome, Antioch, Ephesus, Athens, and Corinth.
- 1) The Marcionite movement, which grew from the Apostolic Movement (A-2) and had a written gospel incorporating synoptic sayings (A-1).
- 2) The Valentinian movement and every other early gnostic group, which grew from the Jewish Gnostics (A-3) and either used a synoptic-like gospel (A-1) or decided to write new ones (such as the earliest forms of the Gospel of Thomas and the Gospel of John). They also, for the most part, used and interpreted Paul. Greek texts were used throughout.
- 1) The Marcionite movement, still around. Based on Paul and a Gospel. Septuagint not used.
- 2) The Valentinian movement, still around. Other gnostic groups, still around. Septuagint used loosely, if at all.
- 3) The proto-catholic movement (the "progressives"), with strongholds in Rome and Antioch (and inroads into Greece and Asia Minor), pressing for the rejection of the letters of Paul, for the retention of the Septuagint, for the use of the gospels as scripture (whether in Syriac or in Greek), read literally and non-docetically. Justin and Tatian belong here. So does Hegesippus. Papias goes one step further than that, with his stated preference for the orally-repeated sayings of Jesus.
- 1) The Marcionite movement, still around.
- 2) The Valentinian movement, still around. Other gnostic groups, still around.
- 3) A less-than-fully-catholic movement, also known as the Jewish-Christian movement, who retain the sol evangelium idea, typically in the form of a Syriac gospel ("Gospel of the Hebrews") or Diatessaron.
- 4) The fully Catholic movement (the "great compromise"), promulgating chiefly from the city of Rome (and installing cooperative bishops around the empire), determined to use four separate gospel texts, in Greek, and their version of the letters of Paul, but to read the gospels literally and non-docetically (and with interpolations). This way they defeat the gnostic groups, the Valentianians, and the Marcionites on their own turf.