Level 4 focuses on finding or creating highly predictable environments. This is what allows for automation. By regularizing the environment you can structurally eliminate the edge cases. It works like a virtual rail system. That works. That's the future. That's the way that automation itself actually happens in the real world.
I think it will be pretty easy for Level 5 to be an improvement over human drivers that get tired. And let's not forget that some number of people decide to drive drunk and high, along with a whole host of other factors. In total, somewhere around 35k people die per year in auto accidents. So I think FSD has a pretty low bar to beat.
