A slam at Philly. The small item missing is the difference in International O&D between the 2 airports. My bet is that this move is related to Post merger and/or OW planning, else why would US/*A Add/Duplicate seasonal, low yield flights at all, rather than expanding to new international destinations? On the other hands, it could also be the first step in an assumed merger GO to make CLT =ATL and dehub PHL, or simply Parker's temporary reward for CLT/NC not joining the DOJ. Temporary, because these routes will likely disappear before they start if the merger is approved this year, in favor of PHL/JFK - assuming the plan is to re-structure PHL to support a OW international hub. Whatever the reason, this move seems to subtly signal that CLT will continue to be Parker's favorite son and a major player in US's plans.
DL uses ATL as a connecting fortress, and JFK as a large O&D operation for Intl. flights. Sure, they also connect people into JFK for those intl flights, but not to the degree that they do at ATL.
The same could be said for CLT, which is very heavily biased towards connections. If it allows US to focus on O&D traffic at PHL, along with a smaller percentage of connections, then there's nothing wrong with that. PHL is strong enough to stand next to JFK as a OW hub, especially considering the slot limitations placed on JFK operations. US at PHL serves more TA locations than AA does at JFK, due in part to them using a lot of their slots for near hourly service to London.