Yes. Those are the specific conventions that the betriebsrat (Workers Concil) decides, but this varies from company to company and state.
My point is, considering this specific arrangement of 7 hours a day/workday (35h), what would be the offset comparing this same company with 28h/week (4D) with another company not in that arrangement in scenarios where throughput per hour matters?
It's the law, it's the system, so of course that is what they are going to do.