The rank was a short-lived scheme for non-commissioned aircrew to give them their own structure, not far removed from the US Army CWO idea. It lasted barely 4 years and the result was that the only surviving rank was the Master Aircrew, which you mention.
From Wikipedia, about MACr ‘This rank is the sole survivor of a system of separate ranks for aircrew which existed between 1 July 1946 and 1950 (another system for technical staff existed between 1950 and 1964)’.