I suppose it depends on whether you, like the author of the linked article, implicitly define "words written about" as synonymous with "the flow of publications

I suppose it depends on whether you, like the author of the linked article, implicitly define "words written about" as synonymous with "the flow of publications", translated to sales of mainstream hard-copy published books. Google Trends is one way, sure, but there's also Fanfiction.net, which contains some 8,932 entries in the Harry Potter category. Some of those are compilations, some are just a couple thousand words, but many are super-novels at hundreds of thousands of words. You don't have to do much math to realize that's orders of magnitude larger than five biographies and 'several' publishers eyeing the 20-year expiration.