The fundamental problem with this is that the economy is made up of intelligent people who can actively find ways to exploit flaws in the model, and that - beca

The fundamental problem with this is that the economy is made up of intelligent people who can actively find ways to exploit flaws in the model, and that - because the model's assumptions make it hard to become filthy rich - they have a direct financial incentive to do so. So, in practice, the interesting parts of the economic system all rely heavily on breaking those nice elegant assumptions.