I’d say it’s what we know about US OT criticism today - Enns himself complains about English scholarship not following suit. And I’m English, Reformed and in the Catholic tradition!
Late Patristic figures like Origen and Gregory are indeed ancient authorities, but the historical understanding predates their allegorical one - for example, Josephus is happy to recount the death of the firstborn (and the existence of Adam) as straightforward history in Antiquities.
But I’d say we know far more about history than him, or Gregory, or the nineteenth-century critical scholars. On the one hand, we understand more about the literary genres, the use of hyperbole in military accounts and so on, which casts some light on the Exodus account.
On the other, whereas Gregory had only the Bible itself to rely on, we can say that, for example, the destruction of Jerusalem and the exile consistently foretold by the prophets as divine judgement actually occurred in exactly the way Scripture describes. Likewise the subsequent destruction prophesied by Jesus in vindication of his ministry also occurred (not least because described as history by Josephus), and has historical ramifications affecting the world down to the present.
This interweaving of God’s actions in history makes it pointless to lean on “fictional typology” - Jesus’s kingdom is presented by him as the restoration of the remnant of Israel after a very real historical, as well as spiritual, exile for covenant-disloyalty. That major emphasis alone would be sufficient to make the more distant typology of Adam less than crucial, much as it’s really no use getting steamed up about the moral impossibility of the destruction of the firstborn when the actuality of Jerusalem’s two destructions is staring you in the historical face.
So if the exile-judgement prefigured in the “Old Testament of the Old Testament”, ie the exile of Judah which became typological for the kingdom of Christ, was historical, the question of whether the type itself is literal or figurative is a matter of evidence, not principle.
Enns says that the Fall narrative was a response to the Babylonian Exile: Tom Wright says that no exilic Israelite could have read the Fall narrative without identifying Israel with it. Which way round is it?
Apart from the positive evidence of the re-use of Genesis themes and language in the pre-exilic prophets, I just don’t see what function the Eden narrative would serve as a new-made tale told to exiles. The main thrust of the prophetic agenda had been, for centuries, unfaithfulness to the covenant and the law especially in idolatry, and the prediction of nasty foreigners to finish off the covenant… mitigated around the actual time of the exile by the hope of an entirely new kind of covenant.
If you’ve been led away to Babylon, that point has been more than amply made to you: you’re writing and reading Lamentations. Or if you pick up on the latestr prophetic word, you begin to pray for a distant deliverance, or at least the hope of return after 70 years.
The returned exiles live in the day of small things and, to most, continued spiritual exile, and begin to focus their hopes on Messianic and related eschatological expections.
So somebody makes up a human origins account in which the first humans mess up as throughly as the chosen people appear to have done. If I were a Jew, I’d say, “So what? That doesn’t ease my pain, or give a way back to God.” In fact, given that I already knew the story of Adam (as suggested by Hosea and Ezekiel, at least, not to mention all the other literary allusions to Gen1-11 - even the source critics attribute Gen 2-3 to J), I’d be mighty suspicious about the validity of a new version that made my unprecendented suffering merely the story of Everyman.
That’s even more so, it seems to me, if one follows the Orthodox Tradition that says the Eden narrative explains death, not sin. How does your exilic Jew relate to that typology in his hour of greatest need?