> The watts per task is abysmal compared to a desk calculator.

It depends on the calculator and task at hand. Consider graphing, integration or any programmable needs, and they might converge. ALU of a processor is pretty efficient at what it does.

> The app is less efficient only in an abstract, impractical way.

Again, depends, as I said above. You tend to brush efficiency away because you only mentally measure time to completion, only, which is understandable.