An unvoiced assumption that people were historically more literate pervades the entire article. As a former lit. major I used to buy into this kind of thing. But I now think this belief is the product of profound selection bias. Literature and history libraries are full of the very best diaries and letters of the very best diary and letter writers because those are enjoyable to read and being more detailed are more useful. History is not written by the victors but by the literate.
People of letters that write this kind of article are obviously inclined towards letters and therefore inclined to sample history through literate means and therefore greatly overestimate the literacy of the past.
But let us pair anecdote to anecdote. There is a podcast network called "The New Books Network". It examines weekly the release of new academic works. It began as "New Books in History" covering one new history book each week. Now it features dozens of podcasts each covering a new book every week. Engage these podcasts for six months and at the end, tell where your biases lie. You will probably suddenly believe we live in the most literate age of all.