I would reach a different conclusion than you based on the flaws you identified, namely that argumentation and language is a flexible instrument in the first place. If I was reading a (peer reviewed) history text and the author suggested something like the Great Depression had one cause, frankly I would put the book down.
According to Wikipedia the most famous book on the depression, Friedman and Schwartz's A Monetary History of the United States, 1867–1960 offers a single cause for the great depression, falling money supply. That might be right or wrong, I don't know. But I know that Housel's "it was a lot of things" is lazy thinking that sounds like wisdom.
