GC, then unfortunately it seems that the number of airlines you consider might drop by at least one more.

If you read through the thread above, QR has taken this approach to such cases for at least 3 years (if not longer). Some QR check-in agents even deny QR-to-other-OW cases and seem to need the policy highlighted to them (or a manager) before they agree to the request.

Perhaps in smaller outstations where they use third-party agents you might get a different result, but it does appear that QR staff have fairly limited discretion on top of what is stated in their published policy.