With OWE and GE economy fares, Qantas has told me it grants status credits only as per discount economy rates rather than for Y, which seems to rule out a status-maintenance run on a QF OW ticket, which is apparently booked in M.

Does this seem correct? At that rate, you'd have to go around the world four times on a OW Y fare in order to amass the same number of credits as one trip in J would give you.

Qantas said that it is impossible to buy a genuine Y OWE or GE fare in order to obtain Y-type status credits. Seems a bit odd.