brized

Suppose you're a factory owner with 4 workers working 40 hours per week.

Your analogy doesn't work because its premise doesn't apply here. This article regards knowledge/creative workers like programmers and engineers, not line workers like retail and factory workers.

In line work, the hourly threshold at which you see diminishing returns is much higher compared with knowledge/creative work. There's also generally less need to be physically present at work as a knowledge worker, while as a line worker it's inherent to the job.