5/4 isn't that challenging of a time signature. I would argue it's just uncommon and so most people associate it with Take Five. 3/4 was extremely popular in Europe for centuries and is not perceived as challenging.
The article is making the case for challenging music. You pointed out that Brubeck made challenging music (i.e. 5/4) accessible to most people. My argument is that this is a poor example as 5/4 is not that of a challenging time signature, and most non-musicians who heard Take Five probably didn't even perceive the uncommon 5/4, and just enjoyed the tune. 5/4 is popular in progressive rock, post rock, and electronic music. In my experience most people do not pay attention to that. Similar to 3/4 - it's an uncommon but easy time signature that people in the Western world have no problem with. Basically, there is no challenge.