I think my confusion is more about Uber’s incentives here. They’re providing a ramp-up platform for Waymo as you described, but as soon as it hits any scale Waymo can easily part ways.
I don't think Uber has anything to fear from Waymo:
(1) It will take years for Waymo to ramp up to "independence" scale. How many cars do they have now, and how many would they need? How long will it take them to negotiate new regulations with every city and state? 5 years?
(2) This deal is probably not exclusive. Uber can strike a similar deal with Cruise as well. Uber becomes the Amazon of driving services, a platform gating access, with all the data.
(3) Having a big money company behind them is good. And if Waymo acquires Uber in 3 years, it's not necessarily a bad thing for Uber.