Problem is you need a lot more crews per aircraft in longhaul operation than doing shorthaul. For example for our "pure" shorthaul fleet we calculate with an average of five crews per aircraft but it is possible to get away with four for some time until they are burned out, then it skyrockets to around seven.
For our mixed fleet operation (A320/A330) we calculate with around 7,5 crews per longhaul aircraft, if we operate it as a pure longhaul fleet it would be around 10 to 12 crews per aircraft. If nearly all flights need an augmented crews the numbers will be even higher.
Those numbers are of course without the usual overhead of management and training pilots. So all in all it is a tad higher, depending how many trainers are needed per aircraft.