you said "if I join QF Frequent Flyer I can only earn points on CX on certain classes, which happen to be the more expensive economy fares"...
I assume fare classes that are not in the list you mentioned would earn miles in QF's program...the "less expensive" economy fares won't earn you points in QF, but those won't earn you points in any other programs either, include Asia Miles...
if that's the case, QF's program is as good as CX's...the only question is, 70% vs 100%...and that would change to 100% in September anyway, right...