The State of Registry is the legally binding authority along with their regulations under their laws. This is what is paid for through these authorities by the aircraft owners, and this is what is legal and correct from an airworthiness, operational and regulatory viewpoint. If this is to be undermined or if two sets of regulations are having to be followed, then it ultimately clouds the area of flying legally should an accident occur.
Also, are you saying then that Ops manual templates currently being worked on by some private register CAA's are likely to be useless, and that another countries more onerous CAA Ops manual regulations need to be followed ?
I find this highly unprofessional both towards the operators concerned and to the extremely well qualified professionals currently writing the templates, for use by the operators on their private registries.