I would be interested in the sources you used to arrive at 20 hours a week. That is less than 3 hours a day. I can't imagine any study of working hours would come to a conclusion that was such a round number more like 19.6 or 20.3 and I can't imagine is was uniform across cultures. Farmers worked dawn to dusk during harvest.

I certainly do value all labor equally. We can debate which kind of labor are more valuable. Skilled labor be it life saving medical care or technologial skills are more valuable than unskilled labor and if you don't reward skilled labor better than unskilled labor you will not have enough people investing their time to learn skills.

TEK