It doesn't say that economic output would decrease, only that luxury goods sales would decrease. I will take this misunderstanding into future consideration. It is also a misunderstanding to assume that "the other countries all copy it better": the implication is that when the first country uses the system, it buys fewer luxury goods from other countries as well. However, people would be more divided on the benefit of a country BUYING fewer luxury goods. If people want expensive German cars and they can afford them, let them, right? But everyone in Germany presumably wants Germany to SELL more luxury cars.
Also, in regards to whether an unused system could be beneficial, it's worth pointing out that the overtime system was basically invented in the 1930's, during the Great Depression. Companies suggested it as an alternative to further mandated decreases in working hours.