I was providing a very basic example -> and yes, useragent can still be useful. But agreed, further feature detection, which the article calls "fingerprinting"

I was providing a very basic example -> and yes, useragent can still be useful. But agreed, further feature detection, which the article calls "fingerprinting" is needed if you implement anything beyond the most basic patterns. But even basic patterns are helped by some minimal detection. Text only / braille readers etc can be targeted nicely as an example.