The single biggest improvement is achieved by a lower seat mile cost. The 77L is 10-11% more fuel efficient than a 343 with comparable capacity, and the 77W is 25% more fuel efficient on a seat mile basis than a 345. The 77W basically has the same trip cost as an Airbus widebody for comparable seating and cargo capacity only it handles even more passengers and cargo. Any use of the extra capacity, even at deeply discounted rates, is incremental. So if AC sells an extra 20 seats and 5 tonnes of cargo on a flight, that's gravy. While AC has to pay a higher ownership cost for the 777, it has put some equity on every aircraft to reduce the financing charges and the 343s are being sublet for premium rates. The 777s are also in their warranty period.