With BA, CX is in the "not friends" list of mileage earning. You will earn more miles and probably be treated better on BA, as you will easily hit GGL. And while not as convenient you may wish to consider JAL, QR or AY as they are all in the "friends" of BA list.

I find CX as a BA OWE to be solid with some recognition, but certainly are behind CX elites in access to seats, compensation, and disruption etc etc.

While not sure of the amount, rather than ask for an upgrade, opening an AM account and asking for the amount of miles that equals an upgrade may have been easier for them. That said CX are recently annoying with switching FF accounts so it may be with a degree of annoyance.