Silmarillion Writers' Guild

I'm glad I'm not the only one who finds it a puzzling (short-sighted, as you call it) that Tolkien was so troubled by the mythical nature of the Music of the Ainur, Beginning of Days etc. He's the guy who gave us Mythopoeia, after all, proudly declaring that myth didn't have to reflect factual reality in order to be true! Like you, I tend to interpret the "flat world" depictions of the "Ainulindalë" and later chapters as a sort of traditional allegory, not necessarily sacred but certainly honoured. Even if it isn't literaly "true", it must have served as an explanation for the existence of the universe (just like other, real-world creation myths did) and formed the basis of the Eldar's self-identity. As such, even when (as Tolkien says in "Myths Transformed") the Eldar or at least their scholars were told (by the Valar) or learned (by observation) that the world cannot have been flat at any point, or that there are a couple of plot holes that the Ainulindalë cannot explain, it is perfectly possible that they would have stuck to the old story simply because it was part of their cultural heritage...

I really love your idea that Eru has to enact being surprised and upset by Melkor's rebellion in order to show the other Valar (who are indeed described as limited to their specific fields of expertise -- in "Of Fëanor and the Unchaining of Melkor", we're explicitly told that "Manwë was free from evil and could not comprehend it") that what Melkor is doing is not acceptable, even if Eru himself designed Melkor in that way! While I didn't let the apparent contradiction between Eru's "no theme may be played that hath not its uttermost source in me" and his reactions to Melkor's themes bother me too much, it has always been something that didn't make sense to me. Your speculation would explain it perfectly, though -- thank you!