You know there are two ways to interpret that quote.
1) Whoever has the most fun, is the best climber. Obnoxious hippy interpretation. "BRAH! Im TR dogging a 5.7 but its so much fun!!!"
2) The better a climber you are, the more fun you have. The world's best climber, is the one who has the most fun, cause you can climb shit that no one else can touch.
I knnda think maybe meaning #2 is the one Alex subversively meant, cause he was "the world's best climber" there for a while it seemed. "You can't bring Alex - that's cheating!"