but it cost more to a330 and 767 as well as 777
I don't think 3 types is necessarily too many long hauls, especially when you're the size US+AA would be. Many, smaller, airlines around the world have many types. BA, for example, will soon be operating the 747, 767, 777, 787 and A380 on long haul routes. What AA needs to do (and is committed to doing) is streamlining their short haul fleet - as that's where the largest losses are made.
The A350 will be replacing US's A330s and the 787 will be replacing AA's 767s soon anyway - again increasing efficiency. 64 NG wide-bodies are on order with the two airlines, if all were placed with a single manufacturer you're just extending your EIS completion. An assignment AA can ill afford.