Reducing the size of the government just makes it where billionaires and corporations control everything instead, which we're already seeing now. You'd need a way to reign in their power/wealth as well.

+1... Reducing government is part of power reduction, not the sum total. To reduce the size of government you need to reduce the size of things it manages. So, for instance, anti-trust would need a huge buf in enforcement to eliminate concentrations of power in business. I'd think strongly progressive inheritance tax would cover the rest.