Uber makes a nice profit in mature markets, but that does not mean their current margins are sustainable. Its hard to imagine a future where they don't pay drivers more.
> People tend to underestimate the true ownership cost of their cars, and Uber uses that to make them believe they're making a lot more per hour than they actually are.
That isn't an argument about its efficiency though.
Maybe the marginal value of a car self-driving itself somewhere is $1 and the marginal cost of that driving is $0.99—it's still more efficient for that car to drive than not. Whether the owner thinks their profit is $1 or 1 cent doesn't really matter.