I don't work for EK, but I believe the system is as follows.
Routes are bsed on a bidding system. There are 12 groups. Each group is on a list.
Group 1 gets priority for their flights, then group 2, 3, 4 and down the list. Usually group 1 get most of their requested flights. At the end of the month, the group who occupied 1st place, moves to 12th place, and each group moves mup the list. This gives each group one month in the top spot.
Apparently their rostering system looks at all preferences firs, then allocates remaining sectors where there is a gap.
The feedback I have gotten has been quite good.
If I am wrong, or the system has changed, my appologies, hopefully, current EK crew could shed some light on the bidding system.