As someone who flies the Atlantic regularly and has done since the early 90s, AA have thrown away the advantage they enjoyed through their own complacency.
Not quite, their business model fundamentally changed. They killed the Pan Am / TWA model of feeding B747s at JFK to Europe by flying B767s from ORD/DFW/MIA directly and more often and in newer equipment. They had an enormous European presence which has since been downsized massively. The current business model, and one which does remarkably well for them is to code share on BA out of LHR both East and West. Hence MAN retains the ex US PHL route but ORD was left to wither on the vine.
As for UA to EWR, some interesting seat plans showing up in one GDS starting 23rd May, so looks like they could be ones to benefit from AA pulling JFK.....
So 789 or 772 then? Tell us, you know you want to......