While I don't necessarily agree with his take, I guess I don't see where he's "excluding" Paul from Christianity.
As for me, just as an example, I find myself uneasy about some of the discourses in John's Gospel -- there are places where I suspect that, rather than Jesus' own words, we're getting John's gloss on Jesus' words, to address arguments that date from the decades after Jesus' ascension. (I'm not alone in this. In his commentary, William Barclay sometimes discusses the objections to which the Evangelist must have been responding in a given discourse...)
This doubt doesn't affect my trust in the overall legitimacy of the discourse, much less John's Gospel in general, and even less my trust for the overall body of Scripture.
Am I somehow not a Christian if I see more of John in some of those places, than Jesus?
If you're rejecting John dismissively as "Yochanan of Patmos" and saying that his Gospel has nothing to do with Jesus, then this isn't Christian.
If you are indeed accepting "the overall legitimacy of the discourse" and not rejecting the Gospel of John as an imposture alien to the true Gospel, then that would fall within in the scope of Christianity, in my view.