It's likely that the commenter has read less than 5 million posts worth of text though. So perhaps this still points to a lack of diversity in content.
You got me wondering. Supposing the average post is 10 words, and a typical page of text is 250 words, that would only be ~50 pages of text a day over the last 10 years. Which I don't think I manage, but over 20 years I am probably in that window.