I think a significant point in the 996 is also to ensure people are available, not only productive. Most probably are extremely productive few hours per day (let's assume 4) and few days per week (let's also assume 4). We could all be performing almost all our weekly tasks in about 16 - extremely targeted and focused - hours. SO it might be easy to think we should only be working 16 hours per week and that would be enough.

Yet, if people were only working 16 hour per week, the company would stop to a crawl. Because during my extremely productive, I might need a few non productive hours from you. Maybe it's answering a quick question, maybe is giving me a pointer to something, on inviting me to a document, enough that I can keep progressing without being blocked and getting those golden 16 hours interrupted and wasted.

The point is that, even tho these are not productive hours for you, they are creating a massive value for the company because you can be supporting other people productive hours. And maybe those are happening on a Saturday from 6 to 9 PM. In fact it might even be OK for the company to tire you a bit, to get that availability, even if that means you won't have 16 hours of quality work anymore.

This is not in defense on the 996, but it is to balance the whole point that people should only be working when they really are productive/focused/.... Availability, even non productive does matter as well.