I think this article would be better if it abstracts "deep reading" to longform content. The sort of reading the article is focusing on (novels, fiction) is only a small subset of the total amount of "dense" content available. The article calls itself a "frivolous" blog post, but many blogs are very insightful and intellectually stimulating. If in any given year you read zero books, but you read several articles from The Economist and Foreign Affairs each week, you're still reading a substantial amount of longform content.

Even in that (more generous) context, I think it's pretty difficult to say anything meaningful about how much reading the average person does. The best we can do is probably trade anecdotes because self-reported survey responses could be unreliable. That being said, in my opinion a lot of people (especially on websites such as this one) don't have a good awareness of how many people are either inadvertently or willfully uneducated because they simply don't want to read. It's very difficult to replace the information density of longform content when you're using a video medium, but videos are clearly far more popular. Consider how often you search for reviews or instructions and can find only videos on YouTube that say in 5 - 10 minutes what could have been written in a few paragraphs and read in maybe 2 minutes. Sometimes instead of videos it's weird infographics filled with gifs.

Note that I'm not talking about informational entertainment videos or visual walkthroughs - I'm talking about strictly inefficient videos designed to be a learning utility, like all those oddball ones where someone (poorly) narrates how to do something on their compute by recording themselves doing it and typing instructions. Likewise, if you read through the comment threads about a new movie in /r/movies, you'll come away with far more actionable insights about the film than if you watched any given video review about it online. The videos that do have a lot of information density are notable as exceptions that prove the rule: they're generally very long, by YouTube standards, and not (intentionally) funny. Consider 3Blue1Brown or AltShiftX, for example. The antithesis of this is local news or quick video snippets taking the place of longer articles in the NYT, WSJ or FT.

If you're reading this comment, you are probably a person who likes to read. You might not read fiction much, but you're spending your time on a forum specifically devoted to discussing thought provoking content. That means you might be in a professional and personal bubble where all or most of the people you talk to enjoy reading "interesting" things, for some definition of interesting. But most people are not scientists, entrepreneurs or software engineers debating the finer points of e.g. driving automation on Hacker News. Many people (especially below the poverty line) simply don't have the time to read anything nontrivial between taking care of their family and working one or more jobs. Worse still, many people have become so used to video content that they won't read anything. One friend of mine only keeps up with the news by having CNN on in the background at his computer. When I sent him an article about something I thought he'd find interesting (the article on here recently about Riot's anti-cheating systems), he simply said he wouldn't read it - not because he wasn't interested, but because, "meh, too long."

And this circles back to my original point - whether you consider only fiction or any intellectually stimulating longform content, it's clear that the vast amount of actionable information people consume is presented to them via a medium that is not designed for clarity and density. If all you consider is fiction you might miss this point, because entertainment-driven media can be substantially thought provoking whether it's read or watches. But non-fiction suffers dramatically when it leaves the written medium.