The OP may be onto something.

AA's joint venture partner, BA flies a mix of 747s and 777s, along with a few A380s, on most of its LHR-USA routes. A scattered few are flown with 787s or 767s.

So why would AA fly gargantuan 77Ws, which seat just over 300 passengers, on such key LHR routes as JFK, DFW and LAX? Well, AA and BA jointly set fares, schedules and capacity, so if AA's 77Ws are "too large," then not only AA management is out to lunch, but so is management at BA.

Imagine that - the two dominant airlines between the USA and London, flying planes that are "too big" according to the OP. What are AA and BA managers thinking?