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.
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Pareto efficiency might be more useless than "calculate the physics problem assuming air resistance is negligible"
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.