Put me on a C++/asm project and I'd have a hard time making heads or tails of it. So what? Your comment comes off as very angry without any meaningful critique of the article's central topic other than you had a hard time understanding it.
1rem is equal to the same number of pixels anywhere on a given page and, generally speaking, across pages on a given site. If you don't know what the value is it only takes a minute to find out. If you're writing CSS that'll be used on unknown pages, you either a) shouldn't care and just scale relative to whatever root font size the consumer set or b) should set your own size/scale, at build time or with custom properties. REMs have been around and standard practice for 10 years.
1rem is equal to the same number of pixels anywhere on a given page and, generally speaking, across pages on a given site. If you don't know what the value is it only takes a minute to find out. If you're writing CSS that'll be used on unknown pages, you either a) shouldn't care and just scale relative to whatever root font size the consumer set or b) should set your own size/scale, at build time or with custom properties. REMs have been around and standard practice for 10 years.