"Driver is mostly disengaged, but then must intervene in a sudden fail state" is also one of the most dangerous types of automation due to how long it takes the driver to reach full control as well.
Yeah, I don't drive but I would think it would be worse than actually paying attention all the time
You are required to pay attention all the time. That's what the "supervised" in "FSD (supervised)" means.
FSD stands for Fully Supervised Driving, right?