When I first read about this devaluation earlier in the week, I was ready to cut up all of my various Amex cards as their AF become due next year.
Upon reflection, if you are not a member of the Qcult, the 'revised' earning rates are still far better than most other products in the Australian marketplace.
From recent redemption experiences, KF miles are worth approximately twice the value of QFF points. For example, PER-HKG J return is 65,000 KF miles or 130,000 QFF points on CX or PER-LHR J return is 190,000 KF miles or 224,000 QFF points + ~$1020 additional charges on EK. KF J award availability is far better also.
Although I am very unhappy about the devaluation, I will still be far better off staying with Amex for most of my spend rather than earning QFF points on my 'free' NAB QF Signature or grandfathered BW QF World (excluding FX).
I currently have the Charge/Reserve and Edge combination at a net cost of $299pa as ex PA cards. At the current earning rates, I am making an absolute killing as most of my spend is in the bonus categories and I am local champion at my local Coles and Woolworths. I also 'earn' enough statement credits throughout the year to offset the net annual fee.
Post April 2019, I will still earn 1.125 KF miles/$ generally and 1.5 KF miles/$ (or 2.0 KF miles/$ when LC) spent at supermarkets, all uncapped. This is compared to 1.0 QFF point/$ on my NAB QF Signature with monthly capping. With KF miles being far more valuable than QFF points, the case for retaining the Amex combo is pretty clear (excluding any merchant surcharge issues etc).
I see that the main changes moving forward will be shifting all my FX spend back to the BW World and all of my telecommunications and insurance spend back to the Charge. Along with earning far less points in general....