Well, every time something bubbles up about free players not being able to play changes or read music, I feel like it has to be trotted out -- like an abstract visual artist has to be Michelangelo in their drawing ability. Sure, some foundation can help, but why do what Michelangelo did? Why play like Bird did, or why sight-read Stravinsky when that's not what your music requires? Or, perhaps a musician can do this but prefers to play free music -- then let them do it.
A sampling of the musicians on that boxed set, many of whom were excellent readers/composers/players in a wide range of settings: Steve Lacy, Bobby Few, Alexander von Schlippenbach, Paul Rutherford, Misha Mengelberg, Willem Breuker, Irène Schweizer, Vinko Globokar, Albert Mangelsdorff, Fred van Hove, Johnny Dyani... and then there are people like Brötzmann and Frank Wright, Alan Silva, and others, who may not be able to read microscopic fly shit on paper but are tremendous musicians in other ways.