Then, who’s the smartest?
 Who cares?

 If it’s the spelling bee judge, she mean who has the biggest memory and best recall.
 If it’s the corporate executive wanting a secretary, she means who’s the best  organized.
 If it’s the army general wanting someone to fight the battle, he means who’s the most skilled with computers.
 If it’s the head of state needing to solve a political problem, he means who can deal  with the most parameters.
 If it’s the chief engineer, she means . . . ???
 

And what about cost/benefit ratio?
 
Both cost and benefit depend very much on the situation.
Both are multi-component measures.
Division by a multicomponent variable is almost never allowed.
So...
The economist must manipulate the several components to squeeze out a single value.
That manipulation is a door left wide open to personal bias.
Caveat Emptor!