The United States Constitution is deliberately inefficient.
The Separation of Powers devised by the framers of the Constitution was designed to do one primary thing: to prevent the majority from ruling with an iron fist. Based on their experience, the framers shied away from giving any branch of the new government too much power. The separation of powers provides a system of shared power known as checks and balances.
Delegates at the Constitutional Convention also wanted to divide power within the federal government. They did not want these powers to be controlled by just one man or one group. The delegates were afraid that if a small group received too much power, the United States would wind up under the rule of another dictator or tyrant.