What would we do without experts? As U.S. workers continue to enjoy a vibrant job market, they should spare a thought for laborers in one category of professional services who remain mired in a multi-year slump. Established manufacturers of Keynesian economic forecasts have entered a prolonged period of secular stagnation. Some may even wonder if they can ever break out of a “new normal” of declining prestige.

At the New York Times recently, economist Paul Krugman valiantly attempted to overcome his history of underrating...