Shouldn't productivity be measured in number of things done where each "thing" is multiplied by a number that represents the difficulty of the task divided by t

Shouldn't productivity be measured in number of things done where each "thing" is multiplied by a number that represents the difficulty of the task divided by the time taken to do it? If hours are the chief measurement, then you can stretch things out to make it take more time. I'm sure this is happening in businesses the world over anyway.