Having "Greeks" spreading the Christian message outside Israel instead of Jesus' disciple makes a very bad case for continuity between Jesus and later Christians about Christian beliefs.
According to who? There was no orthodoxy here, and beliefs were so varied there WAS NO SUCH THING as continuity.
I never disputed that: "beliefs were so varied there WAS NO SUCH THING as continuity". However, there would have been a lot more continuity if Jesus' disciples (& not a bunch of non-eyewitnesses "Greeks") would have converted the early Christians. Aristides, Justin Martyr, Irenaeus & Origen knew about the problem and opted to have Jesus' disciples doing the early Christian preaching all over the known world, contrary to what shows in 'Acts' (at least Irenaeus & Origen knew about 'Acts'!).
So now a contemporary scholar's opinion becomes a credible source!
You have no case against a professor at one of the better universities.
Biblical professor at any better universities have different opinions on almost anything. Attridge's views are not necessarily shared by all his peers, possibly by only a few.
Yes I have a case, based on parts of Acts, and a bit on Paul's Galatians. But I did not see any ancient evidence cited from your Attridge. And Attridge is no more than a Catholic apologist, trying to justify the many takes on Jesus, what he was and did and said, as eyewitnesses' accounts (and NOT from non-eyewitness "Greek"). Attridge essentially explained the apparent discontinuities as not what they seem, but different "understandings" from Jesus' own disciples.
Let's take a closer look at the main part of your quote from Attridge:
The historical reality is probably much more complex. The Christian movement probably began not from a single center but from many different centers
I agree in great part. The Christian movement started in Jerusalem among Hellenist Jews, but quickly after, got extinguished here but also migrated to other centers where it developed in different forms, regarding christology & theology.
where different groups of disciples of Jesus gathered and tried to make sense of what they had experienced with him and what had happened to him at the end of his public ministry.
Do you agree that groups of Jesus' own followers formulated in different ways the tenets of Christianity? I think you do not. The same for me. Others did, Hellenist non-eyewitness Jews, just like Paul.
Each of those groups probably had a very different take on what the significance of Jesus was. Some of them understanding his death and the resurrection experience, if they focused on it, in terms of exaltation. Others understanding it in terms of a resuscitation of the corpse of Jesus, others not worrying very much at all about the resurrection of Jesus, but concentrating on his teaching and trying to propagate that.
Somewhat acceptable by me (and probably you), but for me, this groups of Christians were not including Jesus' disciples. And Attridge takes the resurrection as granted, as a fact which actually happened. WRONG!
"We can see, even in the canonical text, in the Book of Acts, that there were different groups that were in competition with one another."
YES, but the appearances of these groups in 'Acts" are narrated AFTER the Greek dispersion. So our Attridge used Acts as evidence as I do. But he did not consider the Greek dispersion from Jerusalem. I wonder why?
It also happens to match my conclusions for good reasons. Just because you don't accept them does not mean they are not the most plausible.
It looks to me what matches your conclusions is only "The Christian movement probably began not from a single center but from many different centers". I mostly agree with that also.