You are missing the point entirely. Summers is criticizing "New Keynesian" models from the 1980s that are based on mathematically sophisticated DSGE models, in

You are missing the point entirely. Summers is criticizing "New Keynesian" models from the 1980s that are based on mathematically sophisticated DSGE models, in contrast with original "Keynesian" models from the 1930s that were rather more ad-hoc, such as Hicks' IS/LM. https://en.wikipedia.org/wiki/New_Keynesian https://en.wikipedia.org/wiki/New_Keynesian