The "sustainability" argument from this guy isn't convincing. He's saying that, because Uber treats its drivers unfairly, Uber is not sustainable. However, factors that will affect Uber's sustainability are, by definition, factors that will cause it to go bust, and being "unfair" is not one of them.
Sustainability factors include not reaching profitability / running out of money. However, the last piece of the puzzle in Uber's obtaining complete control of the amount of passenger revenue that it keeps for itself vs. pays to drivers is now in place with "upfront pay". In addition to increasing its take rate, it also keeps raising passenger prices while managing to grow ride volumes, meaning that it is keeping a larger share of a larger pie. Profitability is now looking more likely for Uber.
Another sustainability factor is whether or not the federal government is going to force Uber to make drivers employees. But it's far from clear at this stage that that is going to happen. Sleepy Joe is making noises to that effect, but that's all there's been.
So, no, this ex-employee's claim that Uber is unsustainable is not backed up by convincing evidence. That Uber will go under simply because it is unfair is a non-sequitur.