Can't find where I read that. I believe it was a Miles Davis biography I read years ago. I know many Jazz greats thought the same of Monk. When you listen to "Monk meets John Coltrain" you can just see the two of them just making the hardest possible way to resolve what each other was doing. It is almost like they played musical dare for the last 9 months and finally gotten to a place where we got that album.
As a saxophonist I really enjoyed playing to his work, but my keyboard friends would get so worked up. Just look at 'round midnight. The key signature and the accidentals make it almost unreadable. Plus sure we can play in any key but certain one's are easier than others and it seem like it was always the key that couldn't make it harder if one tried. It was always known if you shown any weakness in playing keys that everyone else would keep modulating to try and mess you up.