Excluding Paul from Christianity is going too far.
If insisting on Paul is too strong, what then would qualify as being too weak a standard?
That road leads to Jesus Seminar land, in my opinion.
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?