I don't think they "sold out," it was a much more subtle shift than that, it was a matter of life or death. It was a matter of not rocking the boat. It was a matter of trying to survive with little or no political sway.
I don't entirely disagree, but I would counsel caution with regard to pressing the point too far – we we face-to-face no doubt we'd be bettwre able to express the nuance.
I'm not sure at what level you see these accommodations taking place?
At the grass-roots level, Christians went about their business quietly and discreetly. Persecutions against them were largely sporadic and local, so not all Christians suffered (Tertullian says there were none in N Africa prior to 180AD) ... even so, Christians were executed for not recanting their faith when given the opportunity to do so, as Pliny states.
Doctrine is formed at a much higher level. Again I will say that 'educated' Christians would have had some grounding in philosophy and would use the lexicon of the day to explain and reason their beliefs. Plato was far more accommodating in that regard than Aristotle, Platonism being more mystical and speculative, Aristotelianism being rational and empirical. Aristotle's God, the Motionless Mover, is far removed from the world ...
But then, exclusion from the synagogue must have been pretty major for a Jewish-Christian, and even a gentile Christian might be given to pause, because they saw the roots of Christianity in Judaism? So in that sense it was a 'big deal'.
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Can one say the lifespan of the Ebionite/Nazarene was always going to be limited, not Jewish enough to be accepted by the emerging Judaism, too Jewish to be accepted by mainstream Christians. I've always assumed these and other groups were founded in and around the teaching of Jesus, but lacked the Apostolic commentary – men like Apollo in Luke 18:24-28
"Now a certain Jew, named Apollo, born at Alexandria, an eloquent man, came to Ephesus, one mighty in the scriptures. This man was instructed in the way of the Lord; and being fervent in spirit, spoke, and taught diligently the things that are of Jesus, knowing only the baptism of John. This man therefore began to speak boldly in the synagogue. Whom when Priscilla and Aquila had heard, they took him to them, and expounded to him the way of the Lord more diligently. And whereas he was desirous to go to Achaia, the brethren exhorting, wrote to the disciples to receive him. Who, when he was come, helped them much who had believed. For with much vigour he convinced the Jews openly, shewing by the scriptures, that Jesus is the Christ."
Apollo knew 'only the baptism of John' suggests an early Christian teaching via disciples who were probably at some remove from Christ in his final journeys – so we might suppose there was a 'primitive' Christianity from the time of the Baptist, but not one expounded by the Apostles.
Who knows?
... we are discussing a period when Christianity was the vanquished. That in itself may explain the paucity of corroborating evidences.
What period precisely? I never saw it as 'vanquished'. Oppressed, perhaps, but never vanquished.
