NYC's subway may be much older, but I find it much more effective. Something Beijing lacks are express lines. If you need to travel the length of Manhattan in the middle of a workday, you can easily jump on 2,3,A, or D and get there quite quick. It is not the same in Beijing. Traffic gets terrible and trains are no faster because there are no express lines. traveling to different parts of the city during the day is a major undertaking no matter who you are.
Where Jing-Jin-Ji really excels (and the New York Area really struggles) is in regional train travel. The regional high speed rail connecting Beijing to Tianjin; Shanghai to Hangzhou, or Suzhou is affordable, frequent, and quick. Affordable: last time I was there a one way ride was about $6 Frequent: they run at least every hour, typically every 1/2 hour. Quick: Trips between Cities like Beijing and Tianjin or Shanghai and Suzhou are about 30-40 minutes, and more important use stations in downtown locations.
I don't know if there are any economic impact studies done on this, but the effect to me seems pretty profound. Not long ago, It would be a full day trip to visit Beijing from Tianjin if you are fortunate enough to have a car, and almost impossible to do in a day otherwise. Now it is almost thoughtless to go between the two.