No its not 'obviously inefficient'. And just asserting competition is 'meaningless' isn't actually an argument.

Neither food, nor shelter, nor healthcare are natural monopolies. As evidence by the fact that non of them are remotely monopolistic in places where there are no restrictions. Monopolies in these sectors are created and enforced by the state. Unless you are using a completely different definition from all economists.

Ironically major shops sell stables such as rice below price or at basically 0 margin, just to get people into the store where they might buy something of higher margin.