They are also completely ignoring why airports are called "hubs" in the first place. People travel to the airport from all different directions, it's almost always a fairly long commute by car, bus, or train. Fifty people aren't standing around in the middle of a city all waiting to take the same flight to the same destination.
Semi-OT, but in Hong Kong they have a marvelous service where you can check in for your flight right in downtown HK, check your luggage, and then get on a train for the 40 minute trip to the airport. Since you are checked in before getting on the train, the clock has already started on the "arrive at the airport two hours before your flight" time, meaning that from a travel time perspective, you get to act like the airport is right in downtown.
I would much rather see that sort of service extended to more cities (I assume it exists elsewhere, just nowhere I have been), rather than a chimerical attempt to redesign all air travel infrastructure.