All true. However, a catastrophic failure could render the fuel control switch(es) useless. Therefore the need for redundancy.
You are correct but it is important to differentiate what these controls do.
The cutoff switches close ONLY the fuel valves whereas the fire handles cut off the spar valves and fuel valves, trip the engine generators, closes the bleed valves, isolate the hydraulics, depressurizes the associated engine driven pump and removes power to the thrust reverser isolation valve.
So whilst a catastrophic failure might well remove the use of the cutout switches I think you would be pulling the fire switch anyway and the discussion was the correct procedure in the event of an evacuation RTO.
Boeing do not want pilots routinely over riding the fire switches as an inadvertent pull of the switch requires a massive engineering input. Hence the QRH warning is in bold and lined above and below in red.
WARNING:
Do not pull the ENGINE FIRE switches before the FUEL CONTROL switches are in the CUTOFF position.
I suppose Boeing could have put in a caveat somewhere of 'try not to land without the gear being down', it can be done but only in times of great necessity!!!!
