There have been an enormous increase in people productivity since the days of your grandfather and father, due to computers, cell phones, way better batteries, better machines, better chemicals, etc. What your father could accomplish in a year, you can do in a month. That's the reason competitive economies, like those in Scandinavia, can give employes 25-30 or more days of vacation per year. The payment received during vacation is higher than the regular.
The problem in US is that the majority of profits from the increased productivity went to the CEOs and the major share owners. Taxes paid by rich people have been decreasing constantly in the last 50 years.
Every study I've seen shows that people taking 2 weeks or so vacation are more productive than people who take no vacation.