It's a nice idea, but it can be difficult to accurately assess everything that's involved in most jobs in that way. The handy thing about the symphony orchestra case is that you really only need someone in a symphony orchestra to be good at one thing: playing the music. Which is pretty easy to assess in exactly the way you described. Most jobs are not so singularly-focused, and involve many different tasks, and different people in the same job might actually go about doing it differently. How do you account for all those things?