Yeah, the number of words in the language doesn't prove the author's point at all.

That said, the difference in lexicon size isn't a trick about authorities or dictionaries, it's a real obvious thing. In English one can usually reach for an obscure word to find a near-synonym with a subtle change in meaning - as well as walking, say, one can trudge or plod or amble, whereas in French you'd be reaching for phrases instead. It doesn't limit anyone's ability to express themselves.