It's just a bad idea to make unverified assumptions--either way. I do strongly agree that imperfect scribes mean even divinely inspired texts require some investigation and reflection to be validly and coherently apprehended. That's why I've spent so much time considering the PURPOSE of biblical texts rather than just their explicit meaning. Sometimes though a prohibition of idolatery is just a prohibition of idolatery (and biblical icons imperfect observance of it just underscore the need for investigation).

I've yet to see any noncanonical text supposedly excluded purely due to bias that wasn't a Gnostic pseudepigraph at best and outright forgery at worst. The line between those authors and Joseph Smith is very fine, IMHO. They're in the same ignoble tradition as Christian authors who altered Josephus' work to make references to Jesus declarations of His divinity: Not only did they falsify the record, but giving doubters of "the historical Jesus" a basis to question ANY reference by Josephus has permanently muddied the water. Gnostics consciously appropriated every pagan religion they encountered as a garbled version of theirs (ironically, I think most pagan resurrection myths were imperfect scribes garbled accounts of what Christians consider the Genesis proto-gospel), and did the same with Christianity; most things excluded from the NT are examples of that and/or known forgeries. I think it's more likely that the canon is too large than too small.

Common representations of the vicarious sacrifice by itself are often incomplete, but that's less a failing of the theology than theologians (particularly when people let others do their theology for them). A mere get out of Hell free card shifts the priority from God to man in just the way the gospels forbid. Pardon the retread of old ground, but IMHO the vicarious sacrifice works well as God deliberately creating an impasse between limitless love and limitless justice to manifest His glory by accomplishing the seemingly impossible. That neither trivializes nor exalts humanitys role, but puts its in perspective. As beings possessing the capacity to accept or reject a cooperative relationship with the divine, either choice manifests divine glory on multiple levels, most notably in granting, enabling and accepting our choice. That obviates criticisms such as God being needy, vindictive and/or coercive. The creations of Jeremiahs Potter are more than mere things, but the Potter is certainly not irrelevant either. Theologies of fire and brimstone, altruism, universalism, traditionalism etc. commit the error of making either God or man extraneous to an interaction the gospels explicitly make cooperative. Understand, I'm not trying to proselytize, I'm just saying that the simplistic treatments of the vicarious sacrifice regularly misrepresent and thus aren't an indictment of the doctrine itself; it's just another case of fallible scribes being unequal to the message (too often, willingly).