All models are wrong, but that doesn't mean they're not useful. OP right in that individual firms are often quite inefficient, but the thought is that the mark

All models are wrong, but that doesn't mean they're not useful. OP right in that individual firms are often quite inefficient, but the thought is that the market will take care of this in the long run: either a new competitor will arise and disrupt an existing market, or the shareholders will get rid of the management if the inefficiency is especially egregious. The thing about macroeconomics is that you basically get to ignore the blips because on a long enough time scale, the irregularities start to smooth out. Scientific advances happen in other fields that may significantly disrupt another industry and vault progress forward, so even if for a while things were inefficient, the market catches up eventually. Economics isn't about predicting the future with great accuracy; it's about gathering as much information as possible to be able to make decisions about what to do right now. You're playing the odds, and odds are, companies will be efficient. Sometimes they're not, which is the entire reason we have the stock market.