I guess you do have a point. The concessions are in place to prevent United from being "shut out" on the European side, but EI could probably decide to stop selling onward connections on United out of ORD.
I'm not aware of what routes EI codeshares on out of ORD and to what extent these could be replicated on AA services, either from ORD or from JFK/BOS/LAX/SFO