For about a thousand years, the only form of Christianity was Roman Catholicism. The article on Christianity mentions the Protestant/Catholic schism in the lede. However: it does NOT state that some in each camp did not recognize the other as Christianand in fact some of that still holds sway today, e.g. the anti-Catholic Jack Chick tracts. So we have the idea of historically something has been, but does not state that those adherents do not usually recognize the other side as being part of them. The upshot: Argument from Antiquity is a fallacy no matter how you try to word it. Same with Argument from Numbers.

We could also look at the page on atheism. Nowhere in that lede does it talk about communism (as many people still equate atheism with communism) or wickedness (as even some dictionaries include that in the definition of atheism). So what "most" might "usually" "recognize" as "traditional" isn't necessarily what it actually is, now is it? -