IIRC, the last Master Pilot was a Wessex driver in the late seventies.`
NCA, formally NCO Aircrew does have its origins in WWII and the Geneve Convention, after all they were all statistically likely to be shot down through no fault of their own. To create a career spine that includes Cpls has been tried since and was unsucessfull being universally opposed. That the other services have JNCO Aircrew does not make it right. Amongst the many reasons for retention of SNCO status is the need to maintain recruitment, and the introduction of WSOp first, specialisation second has reduced the remuster from trade cadre of experienced airmen.
Another reason is the need to command authority (on behalf of the Captain) within an airframe at a time when the Captain has other priorities. With the best will in the world, a Cpl or below would be unfairly challenged at providing the authority that may be required on occasion.
AAC do not emply their gunners in anyway near the skill set of the RAF which is without doubt a waste of resource. The RM/Navy can forward a logical argument for their JNCO aircrew but they do not need Air Electronics Operators, Flight Engineers, or Loadmasters, and the RAF are not obliged to price match the lowest common denominator.