The big problem for mainline is the strength of the $A. For years with a near monopoly on the pacific routes to the USA QF basically printed $A from revenue from a very strong $USD and single handedly propped up the business.
Unfortunately the monopoly is over as is the weak $A, add to that the new competition from EK et al and its not hard to see that currently QF mainline is probably losing money.
2 points on this, the $A won't be so strong forever and more importantly why wasn't mainline given the chance to be able to make $$ with a more efficient fleet.
After all, fuel costs are by far the biggest part of overall operating costs...