I commend to your attention an article about the late Steve Brandwein.
I saw him quite a bit at Mechanics Institute but I make no claim to knowing him well. I never played him, and that would have been a waste of his time anyway. (And spared me from being duly dismissed with any Yoda say "at the empty board for an hour stare you should" "lessons". See the article for this.) But observing his analysis discussions with other strong players, often with the latest 64 or Shakmaty v SSSR in hand, and the traffic of the strongest players in the area coming in to play 5 minute games with him made it clear that this was an elite player who for some reason no longer cared to perform in the arena. If he got 20% from Fischer that proves all that need be proved about his ability.