When I talk about more congestion, I'm talking about more cars on the road. What would be absent would be parking. The expectation that I've drawn from my research is that parking would go up a little bit for a little while, plateau at some point, and then go down, but the actual number of cars on the road would go up and keep going up.
The reason the traffic is going up is that there are more people travelling further. Sprawl means more congestion. Sprawl means the average trip is longer. If the robotic services are inexpensive, it's far easier to hop into a vehicle. In other words, there would be more cars on the road, but almost none of them would be parking during peak hours.