This ranking makes a lot of sense to me. Some of the top economists are failed Physics PhDs. Equally, some of the top sociologists and public policy Professors are failed economists.
Larry, Vindicated [Greg Mankiw]
“President Summers asked me, didn’t I agree that, in general, economists are smarter than political scientists, and political scientists are smarter than sociologists?”
Chart of the Day: GRE Scores By Academic Field [CARPE DIEM]
The conclusion - an economics PhD is worth having.