Drop United move 100% of everything to AA for EXP and the benefit of the 8 E-VIPs. This would mean most of your TATL Leisure Coach Class flights could be in Business Class. You would also have access to the wonderful BA Lounges in the T5 at LHR even when flying Coach/Economy and AC in USA when flying AA TATL even on the few occasions you might be also be in Coach. Read up on this site about the AA Platinum Challenge.

AAdvantage really is the Best Airline Programme in the world for Top Tier EXP Members. You should earn enough miles a year for a OneWorld RTW Business Ticket every 12 months even taking into account BA's low rates for Coach flights in Europe.

PS..Clearly you have never flown BMI Transatlantic Business Class IMHO its the Best Business Class across the pond.Unfortunately only to Manchester.