I too have been operating widebodies into HK for years on 3 different airlines. All of them would use VMMC as the alternate when conditions warrant it. Which alternate is closer to HKG ZGGG or VMMC? Which aviation authority would not have accepted VMMC as a legal alternate (too close to the destination) but would accept ZGGG which is exactly the same distance from HKG as MFM
As several others have stated above CX fuel policy is conservative and very suitable for purpose. You appear to be talking out of your rear.