I disagree. It is more accurate to say that more working hours is a continuum of productivity. Imagine that you have two nearly identical software engineers. One works 40 hours per week and the other 41 hours per week. Which will be more productive? Very likely the 41 hour per week engineer. Now, if you compare 50 vs 51, then 60 vs 61, and so forth, the productivity gap will become much smaller, possibly hard to measure after 60. I have witnessed a few young engineers in my career with simply unbelievable work ethic and talents that could work 80+ hours a week for months on end. It was amazing to see, and their output was unmatched.

From personal experience, I worked like a dog in my younger years for two reasons: (1) To become a better engineer, you need to make a lot of mistakes and fix them yourself. (2) Much junior engineering work is just time in front of the screen pounding out simple features for a CRUD app. The more that you complete, the quicker you get promoted.