It's hardly a breakthrough notion that democracy is less efficent than a dictatorship, but since there are a number of nations that can realistically be described as democracies that have been, by just about any definition, thriving
for hundreds of years, and there are no similar dictatorships, it's obvious that democracy, while not as bare boned efficent, as a dictatorship is far more effective.
Democracy is a method of governance.
Capitalism is a method of economics.
The two are not mutually inclusive (witness China).