"obviously has no musical training, and in my opinion, no one without musical training can be qualified to talk, much less write about MUSICAL theater"
Fenchurch I could not disagree with you more.
Many, many people who write and post about the musical theater have no musical training. And yet, having seen all kinds of shows for many, many years, reading a lot about the genre's history and evolution, knowing many backstage trivia tidbits and having extensive knowledge of the theater all would qualify someone to provide interesting insights, whether in casual conversation or in writing.
Do you have any training in world economics, domestic and international politics, health policy, law, or gastronomy? And yet I am sure you have talked about politics, current events, health and food with your friends or colleagues.
Finally, I don't recall Ken Mandelbaum ever trying to pass himself off as an expert in music.
The meat is always leaner on somebody else's dinner plate!