Welp I did not claim that the Bible was factual, simply that it is the basis for the Christian belief. Are you really arguing that the Bible is not the basis for Christianity?
No doubt you'll consider 'logic' to be a "twisting" of your words however, here's how what you stated above plays out: Your premise=bible as basis for xtian belief; that basis is either factual or, nonfactual. If factual, evident converse facts wouldn't contradict it, (but they do). If the basis is nonfactual hearsay, (and it is), then the conclusion is that the "bible" is the nonfactual basis for the xtian belief systems. Further extrapolation yields: such a belief itself as irrational, (lacking substative support and instead relying upon empty 'faith'), therefore the underlying basis for the belief systems of xtianity is 'blind faith', (bereft of substantive evidence to justify such a belief and, actually manifests as personal preference of opinion).
To answer your largely rhetorical question anyway; if several central themes of biblical parables and beliefs were hyjacked and altered by early authors of the "books of the bible", (and they were), then the basis for many of those central beliefs stems from pre-existant paganism, not xtianity. If that sort of 'copyright ingringement' occurred today, certain parties could litigate the Hel out of every purveyor of infringed material for significant damages. As the situation stands today however, the cultural thieves have a centuries-old fait accompli in that regard.