From an operations standpoint, every time UA adds a flight at EWR they're faced with the question of whether the airport can handle it. We've seen them have to reduce arrivals and departures periodically due to air congestion.

Now ORD has their own issues with UA not having enough gates but flight operations capacity is not a problem. Somewhere I read ORD now has the highest capacity of any airport in the world (if I'm remembering what I read correctly).