The thing is using the average as the indicator of how powerful classes are doesn't really work because all those people are average at their own fields. Singling out individuals also does not tell you how powerful each class is because it may be the inherent talent of those individuals. fYeah, problem is, a Knaak pet like Malfurion does not indicate how powerful the average schmuck is.
It's almost impossible to put all these classes on scale.