Sumner's 6%-6%-5%-5% is a very modest expansion in nominal GDP, leaving it far below the trend of the Great Moderation. However, it could be worse. Compare Sumner's proposal to the trend of the "Recovery" from the Lesser Depression.
The growth path the economy is on now is shown in brown, and Sumner's proposed growth path is in green. Of course, the Fed isn't even targeting the 4.3% average growth rate of NGDP since the trough. Moving to Sumner's growth path is not only a modest improvement, it will help prevent the economy from getting worse.