You know, it's interesting: for all my having studied the text and the scholarship, I often forget that the simplest points can be the most persuasive.
Looking at text that definitely comes from Babylonian and early Second Temple times, such as Ezra and Nechemiah, it is actually striking how different the language, the style, the idiom, and the structure are from texts posited to be potentially much earlier, such as Genesis and Exodus. And it's not as easy to dismiss as writing it off to the differences between D-school authors and J/E authors, even with the evening out from redaction. Any part of Genesis or Exodus sounds more like Deuteronomy or Judges/Samuel than it does Ezra/Nechemiah or Esther or Proverbs or Lamentations.
The differences in usage, style, and construction are perhaps not as stark as the differences between Chaucer and Tennyson in English literature, but then, Hebrew has evolved in a far more restrained and nuanced fashion than has English. But the differences here are at least as notable, I would say, as the difference between Shakespeare and Alexander Pope. And that is a very different language: one could not mistake the one for the other.
That convinces me anew that early Torah layers simply must predate the Babylonian Exile: they just don't read like later texts, in any fashion.
But I also have to concur about questioning the shift to monotheism. Such major theological shifts in an entire people don't take place overnight, and don't take place in a vacuum. Given that it seems quite clear that Jews were monotheistic by the early to mid-Second Temple Period at the very latest, how would that have come to pass had there not been a substantial movement toward monotheism for some considerable time previous?
No, it simply stands to reason that there was a progressively more widespread movement from henotheism to monolatry to monotheism that took place during the First Temple Period, finishing in the Babylonian Exile.