I don't think FRMS is the problem per se.
The problem is, most operators don't have the first clue of how a genuine FRMS and it's associated management must work. Either that, or their corporate culture is at odds with a fair and transparent management of fatigue.
Either way, it's probable that the loudest voices in the lobby group are **** scared that they will either f#ck up the process, and/or their abissmal record on fatigue management to date will ultimately disqualify them from implementing whatever it is they think an FRMS should be!
And that leaves them with CAO 48.1
There's the real problem.