Most European routes from PHL are running at 90%+ load factors since April, though I haven't seen the July data yet, I have no reason to believe it's dropped significantly. Other than a few bad days operationally due to summer thunderstorms, I highly doubt these flights are going out consistently 1/2 to 1/3rd empty in J or W. To your other point, while PHL is certainly a big station for the 788, plenty of routes see the 789: BCN, DOH, DUB, EDI, FCO, LHR, LIS, NCE and ZRH. LHR and ZRH are going 789P this Fall as well.