What single-taxers recommend is only one tax, for land ownership. That's the fewest number of taxes - only one. That is not only the most efficient possible tax system, it's the fairest. And the reason is location is the main economic resource every human being uses since we have to sleep on land every day just to live. So, everyone needs the same "deal" (financial relationship) from the government when it comes to land. And while the waste of our most valuable non-renewable natural resource (space-time) will be discouraged, there will be no taxation of wealth creation, which will result in maximum wealth creation. BUT, it will not result in the maximum possible amount of public revenue because workers (wealth creators) will keep all their money. Maximum public revenue is achieved by treating us like serfs, which the current system does.
Your definition of efficiency is based on what will generate the most public revenue, not what will make the economy the most efficient. Efficiency means producing more with less, not just "producing more" regardless of the amount of waste generated.
If society exists only to fund government, yes, tax everything that moves. But if government exists to serve society, it should tax exclusively for the use of non-renewable natural resource (especially urban space-time).
The difference between land and labor is the basis of classical (scientific) economic theory. But "real estate" taxes include a tax on the land AND a tax on the structure. So, gauging the effect of land-only tax with a "real estate" tax is unscientific.
The masses lack equal access to land, their daily source of life. Instead, they have to pay investors like "rent cattle". Neo-capitalism is not free enterprise as explained by Adam Smith and the "laissez faire" economists. We have the same tax system aristocrats used which is why the "property ladder" is like feudalism.