I dont mean to be rude overstress but i dont think you have a clear understanding of the role of the FSM.
It may be that it is different in your airline but our FSMs have a lot of responsibility that the captain doesnt get involved in. such as dealing with aggressive pax, medical emergency, on board fire etc.. if there are only 2 flight deck on board which there often is then one pilot can not come out of the flight deck to get involved so this is why we have FSMs. They are also held accountable for everything from procedures being dealt with right to a crew member not ensuring that they have 2 I/ESBs at there door station when the FSM has to many other duties to take care of at the end of the flight than to walk around to inspect 12 door stations etc.. I have spoken to many FSMs who have faced disciplinary action or been hauled into the office about all these things, they can even be demoted or Taking to court if a pax takes legal action. They are also held accountable for the crews wellbeing and behaviour down route. They need to be given far more credit for what they do. And this is not coming from an FSM, I am a mere senior crew member with not much responsibility.