Monarch Man
To my understanding non of the bio-mathematical sleep predictive models can handle cumulative fatigue (some not at all) so on paper you're comments are solid. I suspect also there is a lack of data specific to EK Operations which any proper FRMS would need.
No FRMS in existence can adequately predict true fatigue, it is a fudge of language and terminology to satisfy regulatory pressure in a litigation prone environment, hence the individual responsibility to be deemed to be fit. In essence if you go to work you are by your actions considered not to be fatigued should anything happen, worse still, if it is determined you are indeed fatigued it is likely then that you will be considered culpable in some form.