Nope, many people level their monk just to do PvP or PvE. So the skilled player to causal ratio of the level 90 monk are extreme skewed.
For example,
http://www.wowprogress.com/post/120_...aiding_results.
Simply put the causal player on a rogue would be level 90 when a monk player will be at level 60, because all monk start at level 1 instead of 85.
Hence the level 90 monk have a much greater ratio of skillful/dedicate player, due to the dedication required.
The amount of monk in upper bracket of arena have not risen despite the number of level 90 have increase is a testament to this.