We don't live in an 18th century agrarian society anymore. The country is bigger and more complex. The world is bigger and more complex. Science and technology are exploding. This all requires a competent and decent system of management, oversight, and regulation. If we went back to 18th century medicine, namely just tying a tourniquet around sick people's arms, cutting a vein and bleeding them into a basin (didn't matter what their problem really was. Who really knew anyway?), then I bet you we could really cut healthcare costs. We could get rid of the air force too, not to mention NASA (I don't see them mentioned anywhere in the Constitution). This was a pre-industrial society, so they had no anti-trust laws. There was no protection of intellectual property. But we could make government regulation less burdensome by getting rid of those too. Illiteracy rate in colonial American was well over 60%. If we are OK with that, we could really cut costs there too. There were no drugs or pharmaceuticals, and getting sick and dying because you ate tainted meat was a minor, and common, problem. No one cared. That was the least of anyone's problems. If you are OK to go back to that, we could easily get rid of the FDA, the USDA, and a couple of other departments too. And if the biggest firearms available were front loading muskets, we could get rid of all gun regulations too. Then we could have a small government again just like we used to.
But do you really think that's how America would be great again? A small, weak, anemic, incompetent government designed for a pre-industrial, agrarian, 18th century world, trying to compete in the technologically advanced, cut-throat, and highly complex global society of the 21st century?