Any job that has no barriers (difficulty, education, licensing) to entry will be eventually driven to zero profit.
Im not sure if this is true, they offered a lot of bonuses if you completed 20 rides within a certain amount of time you get a bonus. They wanted people to drive a lot.
Now, "everybody's private driver" was 2x the cost of a cab (at least) so I think it was a better deal for the drivers. But, to your point, the barriers to entry were owning a black car, being licensed, and Uber vetted their drivers very carefully.
Totally different from what they're doing now.
But, I've also never met an Uber driver -- who used to be a cabbie -- that didn't think Uber was a _better_ deal than driving a cab. If you're a cab driver, you also have to rent a cab with a medalion which was an astronomical cost compared to just buying and maintaining a car.
So, I think this study comes off as disingenuous for not comparing Uber and Lyft to the traditional job of driving a cab.
The real question is how does the richest nation in history think it is OK to pay adults a sub-living wage to do degrading menial labor so that a small number of people can be incredibly wealthy.
But in reality most of the services are used by other highly professionalized companies that operate outside of any traditional legislation. AirBnB is being used by companies to full-time rent apartments in attractive metro areas while avoiding hotel taxes and Uber is being used by professional drivers that don't pay the usual taxi service fees and/or taxes. Because of that both AirBnB and Uber are cheaper than the traditional hotel/taxi service and take away revenue from the businesses that adhere to the law.