You may have access to more accurate figures than me, but looking at seat maps for the next day's departure over a week or two suggests that on some days Economy is doing very well, is quieter on others but not too bad overall. However, filling the 28 J class seats appears to be an issue with sometimes 20 or more shown as available. No idea how many of those J class seats they need to sell at a good price to help produce a decent yield though.
In MAY, I reckon there was an increase in capacity on JFK by TCX, DL (from 22nd?) and AA using the larger a/c of about 13,800 seats. Bearing in mind that the majority of pax are MAN originating and that therefore the first few flights of TCX and DL from the US were probably not too busy, the number of extra passengers in May of just over 8,900 strikes me as pretty encouraging.
You are about right with the 13.800 seats I mistakenly done DL for the full month which does make the increase look much better. I don't have AA specifics but think they did fairly well considering the flood of capacity. Guess June been a full month will tell a better story.