It is exactly as useful. Macroeconomics was completely tangled up until people understood that in a perfectly function economy there was be no business cycle, that even a serious shock would only temporarily slow down the economy. So the focus turned to understanding the market imperfections that make temporary dislocations have such long-term effects.

Physics in idealized situations is incredibly useful, and more importantly, absolutely necessary for understanding non-idealized real situations, so I'm not sure what you're getting at here.