Current mainstream economic theories underfit like crazy, that's their virtue. The problem is, they aren't based on knowledge of what actually happens, but on either a 19th century armchair philosopher's guess at what happens, or principles which have been chosen in order to create an under-fitting model.
So while they don't overfit, they also are't based on any real knowledge of the system.
It seems the other extreme is elaborate overfitting models.
Steve Keen uses fairly simple models, but tries to base them on actual reality (i.e. broad money is created by the banks, not the government, while Ben Bernanke's explanation of the Great Depression apparently focuses on M0, as he accuses the government of not minting enough coins with the gold they had in reserves, with the implicit assumption that the money would be multiplied if the government would only print it. In reality, the money was not multiplied, because the banks didn't feel like lending.)
So while they don't overfit, they also are't based on any real knowledge of the system.
It seems the other extreme is elaborate overfitting models.
Steve Keen uses fairly simple models, but tries to base them on actual reality (i.e. broad money is created by the banks, not the government, while Ben Bernanke's explanation of the Great Depression apparently focuses on M0, as he accuses the government of not minting enough coins with the gold they had in reserves, with the implicit assumption that the money would be multiplied if the government would only print it. In reality, the money was not multiplied, because the banks didn't feel like lending.)