I don't think a literal Adam is necessary for the "sin of Adam" to be a thing, particularly if you're in a mindset already where the purpose of Christ's time on Earth was to establish a kingdom, rather than just to deliver some pleasant homilies and maybe troll a few pharisees on the way to his real intention, which was dying and being resurrected.

In any case, the Bible can absolutely be miraculously inspired and still be subject to critical examination. Looking at the history of how the individual books have been studied, translated, and selected, it's obvious that the text itself had always been very much interwoven with academia and tradition.