The legacy US carriers have gotten away with too much for too long. It's high time there is competition and let the markets figure it out. The legacy carriers have treated loyal customers like crap and now customers are no longer being loyal, they are chasing the lowest fares. It's lovely that AA thinks it can save itself by doubling down on PHL but doing so shows how little it understands that market.
If fares are cheap enough out of JFK, PHL flyers will just drive up to NYC. I get that there are connecting passengers, but routing connections through PHL or JFK makes little difference in terms of cost for connecting passengers.