He did makes his argument. I'm not even a native English speaker and understand dependent vs. independent clauses. I believe there is even a sentence diagram in the Heller opinion.
Regarding your "point" that law students and academics didn't write about 2A, well, as a former Harvard Law Review editor (alas, a mere Associate Editor -- I graded on and was not a cool kid) that would be because lawyers and especially law professors are overwhelmingly pathetic liberals. If you wanted to get published, a pro-2A student note would not be your topic of choice. You'd get blacklisted. Mine was about warning labels and the wisdom (or lack thereof) of having them in foreign languages.
Super-sexy stuff, but I was told, in no uncertain terms, that I was racist to argue that you should not have 154 languages on a warning because you ended up with a book that no one read. I changed what I wrote to something absurd and got my "A" and my federal judicial clerkship.