Why do we think Beethoven (et al) is so great? He has a few masterworks that are overplayed and a vast number of forgotten pieces no one cares about. That really sounds like a lot of performers, classical and current. How do we know who is really great and which of the great old masters is the greatest?
Clearly, one measure of great musician is and ought to be total number of masterworks.But this biases the measure in favor of old>young and prolific>perfectionists who don't publish unless it's brilliant - even if all musicians were equally capable of producing masterworks, with more random draws you'll likely come up with more masterworks. Oh, and should we handicap anyone because of their patron's requirements?
What about percent of pieces that are masterworks? Does anyone know of data on musicians and the percent of their pieces deemed masterworks? The problem I foresee is with (mostly modern) performers who are one hit wonders. That one song may be all they have and they would consequently show up too highly.
A third option is to ignore the masterworks and ask about the quality of the rest of their work. Mozart's 'average' pieces are just so many finger exercises while Bach being mediocre is complex and rich (even if it's the same complex richness he wrote in a dozen other places). I think Rachmaninoff would score rather higher on his non-miraculous works than many others.
The application to economists' productivity is straightforward. Edit: By randomness and luck, it turns out Easterly was also considering the production of Mozart's masterworks the same day. I would not dare to presume to suggest that "great minds think alike," but on occasion, even a Volkswagon and a Mercedes' turn signals will blink at the same time.