I know that, but thats for a comparably small number of large aircraft landing at a single designated location. It wouldn't scale at all to a city-wide air taxi service.
It's not just for large aircraft. ATC manages flights to many smaller airports as well including charters and private aircraft. The system scales pretty well. There's no realistic prospect of having thousands of air taxis in flight at once above a single city, that's just never going to happen and not worth considering.