That is correct that flights on QF are in M, which is disc Y.
So a mileage run on QF has to be very carefully planned with lots of sectors just above 1000miles (eg. LHR/HEL).
So a M-OWE is used to assist status maintenance, but not to gain gold status as that would be very difficult on 20 segments.
Also given that full Y costs almost the same as discounted J, why would you not pay the extra 10% to fly business???????
Mark