Well, that's only valid if the 80% or more of the trip that it CAN handle are known ahead of time. If the 20% of cases that it can't handle are "surprise, there's a deer on the road ahead!" or "surprise, the guy in front of you slammed on his brakes!", then you still have to sit there 100% of the time ready to react.
you need 100% confidence that the care is fully capable of handling EVERYTHING that comes up for the next XYZ minutes/hours/miles/whatever to be able to really have a useful Level 5.
Personally I'd rather be driving the car than sitting there prepared to take over just in case something goes wrong. Until I'm not needed at all for driving, I'll keep the control thank you.