"( You will be lucky to do all that in 2 hours, especially if queues/lines for T3 security are long)"
Security lines at LHR are not really the issue here imo. EK closes it check in desks ( iirc ) at 45 minutes before departure, leaving 75 minutes to collect bags and get to check in. It isn't far from arrivals to departures and 45 minutes should be enough to get to clear customs and collect bags. Once checked in, you should have no trouble gettign to the flight in time
It would be unsporting of AA to not check the bags through, however they are under no obligation at all to do so
Dave