I have read it and I don't agree with it. Nor do I agree that Christianity was predominantly Gentile and was only later Judaized.
What I do think is that the Judaism in the region of Phrygia had been syncretized with the cults of Attis and Sabazios, but was still Jewish in identity. Just as Philo had been influenced by Platonism, but was still a Jew.
I am inclined to think that there was only a Christianity before the 70 CE ( Paul wasn't his founder). Galatians was written very much late, in 68 CE, just before the death of Paul. Only towards the 70 CE some Jews of Jerusalem (the Pillars) became interested about the Jesus preached by apostles as Paul and Apollos. Galatians reflects the threat of the aggressive, recent proselitism by these new apostles from Jerusalem called Judaizers. In other terms, Peter wasn't the real founder, but apostles like Paul were.
I reject these dates completely. All the Pauline letters are post-Kitos, as their author (Marcion) was enforcing the policies of Hadrian. But even he acknowledges that John, James and Cephas came before him, meaning that he was a founder insofar as his own teachings.
The community of Jerusalem acquired influence because the Judaizers became more and more aggressive (=zealously pro-Torah) preachers after the 70, and the same mainstream Judaism condemned hardly the marginal sects before only tolerated.
This is circular reasoning.
]Possibly even Paul was killed by a Judaizer.
No. He died by his own hand in 157 ad.
About Marcion, frankly I don't like who ''judaizes'' him in recent times in order to give him a more prominent role in the formation of the Gospels. I like Detering because he argues for a falsified Paul assuming that the earlier authors of the epistles were Gnostic Gentile Christians, not Jews. Marcion could write a Gospel even as fully gentile.
Then I disagree with Detering here, because Marcion shows a clear reliance on Judaism. Even the more consensus version, which I think is wrong, depends upon Marcion having in some way a Jewish understanding.
The Gnosticism is a phenomenon too much universal (just as the Problem of Evil) to consider it a Christian branch or a Jewish branch. It was simply necessary and inevitable that the gentile Gnostics had to become Christians, as well as interested to co-opt (and de-ethnicize) any other previous Myth.
But what of Gnostic Jews?
The consensus recognizes already the Gnostic interest for Christianity after the 115 CE. I wonder if there were Gnostic Christians even before that date. Surely Philo's ''cainites'' is evidence that there were in Alexandria some Jewish haters of the Jewish God already in his time.
Jewish haters... who were still Jewish. (Possibly Dosithean).