I tend to agree, that nowadays, it would be impossible to make a case for an air traffic facility -airport or heliport- within citycenters. It would make far more sense, I believe, to situate a/h ports at such places where public railtransport is available. Look at all major ports in the world, they invariably have a fast ground transportation to citycenters. It is therefore unbelievable, that Schiphol Airport is planning with Dutch Government, to divert all holiday flights (many ten thousands of flights) to a polder airfield with NO rail infrastructure. What a waste of money.
From a vertical point of view, a modern Rotodyne type could possibly alleviate the air traffic control conundrum in the at area, 20 kms from AMS, by rising above the the AMS traffic and then be on its way.