However, the Qur'an does explain why it's in Arabic. It's because Muhammad was Arab. And so was his community.

Well, duh. For the same reason, the Torah is in Hebrew, the New Testament was originally in Greek, and the Buddhist scriptures were originally in Pali. It's almost as if, to communicate an idea to people, you have to express it in their language. Fancy that!

Did you notice the place where I mentioned that each of the seven "dialects" (sets of meanings for words) and the seven "interpretations" was confirmed by the Prophet as being legitimate? I assume, for some purpose.

I did, but I lack your faith in the value of ambiguity and obscurity, regarding them instead as deepity engines.