If I am not mistaken, MAN-JFK is not BA Citiexpress anymore. Although the crew are MAN based, the flight is BA operated - if you do the following in Amadeus: DOBA1502/03 it does not say 'operated by BA Citiexpress' as it used to.
Also, regarding the performance of BA MAN-JFK, it is VERY profitable. I have been monitoring the loads for the past three months and J,C class are regularly full as well economy, pretty impressive as it is practically only O and D traffic!
From what I have heard, BA would like to scrap MAN-JFK, but it is a real money earner, that is why they do not. Come on guys, if MAN-JFK was not profitable, do you really think BA would have let the service continue? I don't think so somehow!