Top 10 in a vacuum is a silly representation, but saying "Oh it's an outlier it doesn't count" is also goofy--if you're going to balance PVE DPS it should be done based off of what the maximum potential in a reasonable sitaution is.
Keywords - reasonable situation. Outliers aren't reasonable situations. Top 10 represents the luckiest crit streaks, combined with the most buffs fed, combined with encounter exploits, combined with the best play.
Say you've got two specs, A and B. Both, with perfect gear, and perfect play, average 100,000 DPS.
But Spec A has higher RNG variance than Spec B. With perfect gear and perfect play in 25,000 encounters, Spec A's DPS ranges from 85,000 to 115,000 while Spec B's ranges from 90,000 to 110,000.
When you take the top ten results, Spec A will have all of them, and Spec B will have none of them. But by any reasonable measure, the two specs have equal performance.