I often find myself really bad at remembering what I read in a book or blog post or heard in a lecture on youtube or Coursera beyond the larger point, so I'd agree with the author at least that far.

However, when a question is raised relating to something I read, eor a point is stated that conflicts with something that I read, I usually find I can remember where I read about it. Even if I didn't internalize the idea I can look it up pretty easily, and 90% of the time being able to look up something is good enough. So I think whether books work depends on your goal: is it to perfectly internalize something, or to be able to have something you know you can refer to later?