EWR is basically the second major airport of the PHL region, but I don't think BWI has much an impact with exception of maybe northern DE, which might be more of an issue for Avelo trying to start ILG when Delawareans already have PHL and BWI as a fallback option.

From everywhere north of that, BWI is too far, expensive tolls, no regional transit service, and not worth it with a few exceptions. AA really does have highway robbery pricing on some short haul trips, but one has to figure if they drive to BWI to then fly to a city like ROC or CLE, because AA out of PHL is so expensive, they would consider UA nonstop out of EWR first and then consider driving the full distance as options over driving to BWI to catch a short haul flight.