I was led to believe the SNCO status was a throw back from the war. In the event of the cab buying the farm, a SNCO was presumed to get better treatment by his captors than a junior rank.
The argument re SNCO having more credence down the back end is, I believe a non starter. JNCO's have been able to carry out their duties without the added 'weight' of rank. 40 or 6 pax makes little difference if you have one awkward titrash. I don't think I have ever heard of a JNCO rearcrewman being userped because of his rank or lack of it.
I think what you are saying Tigs is that all NCO aircrew; Army, RAF, RN, RM should be SNCO therefore allowing those who are presently not, the ability to be promoted.
Remember, the AAC used to (and is moving back towards), Aircrewman who occupy the left seat. A L/Cpl would have map reading skills that were at times better than his pilot counter part, a tactical grasp of the battlefield that would put many staff officers to shame and have the ability to fire the weapon system onto a target that he could recognise on goggles/thermal out to a distance of 4K's and 9/10 hit it first time. He could operate all the aircraft systems, operate the tac radios along with being able to decifer BATCO. As well as being able to fly the aircraft should the pilot become incapacitated.
We stopped using them because some felt it wasn't correct a L/Cpl leading a Battle Group formation!
Cheap labour but it proves the point a JNCO is actually quite capable of doing jobs other services reserve for SNCOs or commisioned officers.