Instead of field hospitals, they should have equipped LTC facilities with adequate PPE and large scale testing. Positive seniors should have been moved away from the healthy population. The result would have been a fraction of the death toll.
This was the protocol that was supposed to be followed. A SNF was supposed to be following the same protocols and equipped with the same gear as hospitals. They explicitly said that any SNF that could not maintain CDC recommended standards for case isolation should let them know and not accept COVID positive patients. In hindsight, it is possible that this was not a good move.
The reality is that the NYC medical infrastructure is a bunch of individual institutions that do not operate through one central system. If there would have been one central command center coordinating which ambulances bring patients where based on real time capacity data, the field hospitals and ship could have been seamlessly integrated into the network. Being as it is a bunch of private institutions that operate independently of each other, each with their own ambulance network connections developed, this is not what happened. The way it was, supplies and case load were not efficiently distributed. Therefore, the new unnetworked hospitals were left vacant, while the pre-existing facilities were overwhelmed.
There was and still is not a method for an overriding system to assume control of coordination of hospitals in case of a mass casualty incident. This is a major gap in the system.