Not only can you make direct comparison, in fact you should. When you fly CX you have the option of selecting which FFP to credit your miles to. So it is not only valid but also smart to compare the benefits of AM vs. AA. Without question AA offers more miles earned for a given flight than AM. AFAIK, AM's only advantages are upgrade awards on non-full fare economy tickets (plus lounge access which presumably you already have anyway if you're elite). The real benefit of accruing AM miles is not even with the AM program itself but with CX Marco Polo loyalty program. The guaranteed seat reservation is one of these benefits along with higher op upgrade priority. That's about it! Now if only CX allows miles accrual on AA and loyalty accrual on MPC, then that would be great.

In a global competitive marketplace, customers do not make distinctions among products based on where they are in their life cycle. Given choices customers will choose the product that provides them the best value proposition. The fact that SQ and CX's FFPs pale in comparison to US-based FFPs simply reflect the lack of "buying power" that their customers have. So if I were Asia based and have to make do with CX and SQ's anemic programs, I wouldn't be justifying it but rather writing to them and expressing disappointment.