Certainly, the canonical gospels are relatively moderate, compared to the Gnostic gospels or the Dead Sea scrolls. That's why they became canonical under Rome. Just to be clear, the "centrism" that was promoted wan't historical. When I speak of the most likely Jesus "as far as we can tell from the gospels," I don't mean we should take everything said in the gospels as literally true. We still have to read between the lines because the gospels were propagandistic. If there was a historical Jesus at all, he wasn't likely the centrist figure that's portrayed in the gospels. Rather, he would have been a mystical rebel that's only dimply perceived in those texts. His radicalism sometimes comes through, and sometimes it's downplayed, especially in some translations.

Was Catholicism centrist? I think you're right in certain respects, but talk of centrism here may be misleading. Indeed, I've argued against the notions of centrism and of a political spectrum even in the modern case. These are somewhat misleading notions. Sure, Catholicism stood between Jesus's radicalism and full-blown Roman paganism. But Catholicism sided more with the Roman Empire's polytheism and imperial secularism than with Judaism, mysticism, or political radicalism. And the Church ended up being more totalitarian and regressive than the Roman Empire.

American Christianities don't seem to be centrist compromises. The modern context is different from that of the ancient world. In any case, these American forms are more like appendages of flagrantly anti-Jesus/countercultural institutions. I'll take a look at your article, though.