>If you spent so much time at the workplace like the Japanese you end up with a low producivity on paper pretty much by definition, because it's simply output divided by amount of time worked.

It is not as simple as that: in general, more developed countries tend to have higher labor productivity. Japan has been historically low for several decades.

I'm no specialist of labor statistics, but note that Japan actaually worked fewers hours than Italy , accoding to OECD anyaway: https://stats.oecd.org/Index.aspx?DataSetCode=ANHRS. I am pretty sure that most people unfamiliar w/ Japan would not place its productivity as low as it is, close to countries like Turkey or Slovakia.

>Here in Germany we have a similar paper culture (although not quite as extreme) but very high labour productivity

I am familiar with both countries, worked in both, and it is nowhere near comparable. But paper is only part of it. The overtime culture is quite intense. I still vividly remember my first work experience in Japan > 15 years ago, with 3-4 hours-long meetings where half the members, including the lab's head, were sleeping.