"Where is the evidence of that? I've ridden with plenty of Uber drivers who only drive a few hours a week."

If you turn down fares or only drive during certain peak times, you get pushed lower and lower into the queue when the robot decides who to send out on fares.

>This is far from being a dominant factor in employment status. If I offer a job for a fixed rate on Upwork and hire a contractor to do it, the fact that we didn't negotiate the rate doesn't make them an employee.

Except that the person on Upwork has the ability to negotiate, and choose not to take the gig. A driver for Uber does not get the chance to negotiate a fare with a customer and turn it down.