I am all for single payer (Medicare for all for example) but there are plenty of ways the US system could improve. First would be to mandate pricing transparency so we actually have some data on the table for a rational discussion.

The US government is essentially the only game in town for military hardware and contracting, but I don't think anyone would hold up that procurement system as a model of efficiency.

In the world of health care, many developed countries have single-payer healthcare and the US pays twice as much for everything as all of them. If goverment-run health care is inefficient, why is our "free-er" system half as efficient?

My point is that it's probably something other than monopsony effects.

That is one solution to one problem. It has the side effect of overly simplifying American systems of governing and labor, and would cause new side effects or amplify existing ones.