You said: “This concept came in from Rome and there is no sign of it in the early church. The fact that surviving writings from Origen contain the subject can only be coincidental.”
Origen is not the only relatively early theologian to develop a trinitarian theology; Tertullian, writing about a decade earlier, attempted to codify a concept of the Trinity. The deeper origins of trinitarian doctrine are found in the ‘Unwritten Doctrines’ of Plato himself [see J. Dillon, The Middle Platonists (Cornell 1977), and E. Moore, “Middle Platonism” http://www.iep.utm.edu/m/midplato.htm)]. A basic triadic emanationist schema of One-Dyad-Demiurge (or World-Soul) goes back as far as Speusippus and Xenocrates, and is given a central place in the Pythagorean cosmologies of Ocellus Lucanus, (pseudo-) Timaeus Locrus, and others, on into the period of Gnosticism and early Christianity, not to mention ‘esoteric’ Platonists like Numenius (whose works Origen read) and Plotinus, Porphyry, Proclus, etc., etc. …