1. Working less may well not result in getting more (or the same amount) done. The article mentions a correlation between shorter working hours and higher productivity. As always, correlation does not equal causation. Most likely those countries with shorter work weeks are developed countries which have higher output per capita than less developed ones not because working 40 hours a weeks is more productive than working 80, but that utilising a higher level of technology gives superior output.
2. The idea that because the Dutch apparently spend all their free time riding around on bikes means the brits would if given more free time is a joke. We'd spend it doing the things we enjoy (damaging our livers?), not suddenly become some imagined healthier happier version of ourselves.
All in all a pretty poor article I think as a result of the above isssues.