The Book of Mormon an ancient book?

In our ongoing analysis of Mormon apologetics, I will today discuss an article published in Noel B. Reynolds and Charles D. Tate (ed), Book of Mormon authorship : new light on ancient origins, (Volume 7 of the Religious Studies monograph series), Provo, 1982, namely C. Wilfred Griggs effort The Book of Mormon as an Ancient Book, pp.75-102.

Griggs starts his exposition with an analogy (p.77) between how ancient documents are analyzed and how the Book of Mormon should be analyzed (by anyone other than Hugh Nibley). The exemplar is Morton Smith of Columbia's discovery in 1958 of a letter by Clement of Alexandria to an unknown Theodore, discovered in Jerusalem (pp.77-78)---the so-called Mar Saba letter.

Griggs observes that Smith took 450 pages to argue for the antiquity of the 2-and-a-half page letter, and demands similar diligence for the Book of Mormon (p.78).

However, this tack completely bypasses the fact that the Mar Saba letter would have been rejected out of hand had it styled itself as prophecy of future events, in the way that the prediction of the Reformation figures in the Book of Mormon. Modern biblical research is not amenable to prophecy and fulfillment narratives. Thus, it is no wonder that the research into the Book of Mormon as an ancient book is as shallow as it has been outside of BYU, given that the contents violates the most basic tenants of biblical scholarship with respect to prophecy and revelation. Put differently, there is no point in tackling the issue of historical compatibility (p.79) if the contents exposes the narrative as non-historic.

Thus remains the question of what it benefits the BoM to enumerate Orphic and similar parallels to the golden plates and the tree of life (pp.79-102).

A similar tack is taken by Hugh Nibley himself, in his contribution, Two Shots in the Dark, pp.103-142, who goes straight for the Lachish letters from 1935 to authenticate the Book of Mormon. The argument is awash in Nibley's famous erudition and command of the material, but some of the specifics raise questions.

• When Nibley writes: "The discovery of the Elephantine documents in 1925 showed that colonies of Jews actually did flee into the desert in the manner of Lehi, during his lifetime, and for the same reasons; ...." (p.108), this is really puzzling, because the papyri of Elephantine belong into a latter period (end of the 6th and beginning of the 5th), not into the time of Jeremiah. And the papyri I have seen are far too sparse to determine why the mercenaries went there.
• When Nibley writes: "The action of the Lachish Letters centers around the activities of the prophets in the land, who are causing grave concern to the government." (p.110) this is an exaggeration, since the word "prophet" occurs in the ANECT translation exactly once, and in the subordinate role of a messenger; the second mention in Letter VI in this translation is interpolated (and rendered as "princes" in ANECT). 
• Inexplicably, Nibley uses the 4 Esra and 2 Baruch apocalypse, clearly from the first century AD at best, to make sense of Lehi's behavior in the 7th century BC at the time of Jeremiah (p.112).
• According to this paper by Winton Thomas from 1945 on the Lachish Letters, the editor Harry Torczyner himself retracted the restoration of the "visionary man" that is so important for Nibley (p.114) as early as 1940. Furthermore, as Thomas points out, the number of destroyed ostraka in the guard house at Lachish is so high that the remaining can hardly form a set of a conversation, the way Torczyner envisioned it.

What is the point then for Nibley to go into all these other amazing "coincidences" regarding the Book of Mormon and the Lachish Letters as reconstructed by Torczyner, if these problems already make all upstream arguments dubious?