This is a better cocktail than the similar but honey-sweetened De Rigueur Cocktail, as unless you have a very full-bodied honey, maple syrup's 'tang' sits...
You claim that the use of honey syrup in the Brown Derby is a 'misguided belief' which stems from the '33 book "Hollywood Cocktails," but the only evidence you've given that maple syrup was in the original recipe is a column published 6 years later in '39, which uses an entirely different spirit and citrus. Seems a little dubious. Made a rather nice cocktail nonetheless.
Perhaps there is an inference in Mr. Difford's review that the "1930 The Savoy Cocktail Book" describes a recipe for a Brown Derby with maple syrup but "when made with honey this is a De Rigueur cocktail"?