I agree with the broad point of the article, but the author misidentifies what's going on. The author's problems are coming from digital printing, not the print-on-demand business model specifically and Amazon isn't the only company doing it.
The older books were printed using a process called offset printing. It needs large economies of scale to be financially viable, but it produces higher quality books. The newer books are printed with digital printing, which is just a fancy version of the laser (typical) or inkjet printer you have at home. I believe Amazon POD uses inkjet, but not sure. The result is a worse quality book, but also one that doesn't have thousands of copies taking up inventory space until it's sold. Virtually all publishers are moving low volume works this way. The fact that the quality is merely "subpar" instead of unusable is a testament to how much digital printing has improved in recent years.
Separately, paper quality has gone down industry-wide. Paper mills are simply choosing to focus on higher volume papers like those used in cardboard instead of producing fine paper. That means shortages, price increases, and publishers making do. Also, POD publishers don't want to keep every type of paper under the sun. They standardize inventory to keep prices down.
To make things even more confusing, the same work might be printed using multiple methods and different papers, with different inks. It's common to do a first run with POD to gauge market demand and then offset if sales continue. Or offset for a collector's edition, or vice versa to allow more colors.