Your letter should also to Feds since cleary the ATC system is not working in the NYC area. Cleary CO's service could have been a bit better or maybe freindly but they can't do much when ATC rules the day and night.

Planes should not be pushed if there is the potential for this kind of delay. LGA is small and the probably needed the gate for incoming traffic.

OP does have right to be angry. System is not working and plenty of balme to go around.