There is still some time in-between rides where there are no passengers in the car. If riders had a car, that dead-weight car would not be on the road.
True, sometimes it will be equivalent to car travel in that way. But it will never be _always_ true. So overall, Ride share decreases car ownership, but increases traffic.
I'm not sure. The fact that Uber drivers aren't cruising for fares is at least a huge improvement to the way taxis worked. Having spent 9 years in Beijing, it seemed like an even bigger improvement when ride sharing and even just being able to schedule a taxi with an app meant that cars and people looking for rides were connected much more easily and didn't have to go looking for each other (as I often did before).
There are actually places in Beijing to wait for assignments outside of major clogged ring roads and arterials. But it really depends on the design of your city.
