I used to think the same thing, but I did an effort post about this about a year ago (here’s the link)

The article you linked to says something similar to my own understanding: basically, DRM circumvention for personal use is officially not allowed under DMCA and could absolutely be used against you in court, though the likelihood is low. The exceptions the author mentions are pretty nebulous, and the Library of Congress actually addresses the most common cases in their discussions and publication and affirms that they are not allowed.

I don’t personally agree with their interpretation, but I think more people ought to know that it’s officially not legal to circumvent DRM for personal use.