This is not true. Well, true on the surface but not true for real. Slaves and surfs in Rome paid 100% tax to their lords. Not counting lords as the government is misleading. They are government. And if you count them in, and also count in their soldiers and work enforcers and admins, the governments of Rome and tipical western "democratic" government will be very much comparable from all perspectives. Of course, corporations these days should also be counted into gov.