In response to one of my earlier questions about ranking damdai seemed to indicate that player ratings we cross referenced, If that's true, I think you could learn a lot if you used the following 2 additional metrics.
1. His opponent's average win/loss ratio, or rank.
2. The number of unique opponents the player has faced.
However, even these stats can lead to incorrect assumptions. Personally, I think it's a very difficult thing to accurately quantify.