A Technical trade Flight Sgt is still a qualified tradesman so wasn't superior to a Chief Tech as he was simply moving up the trade rank structure, though you might as well call a Chief Tech a Tech Sgt as you no longer have a Junior Tech to play the rank off against, if that makes sense.
Back in the good old days there was a parallel rank structure with Tech equivalents wearing their tapes upside down. Ch. Tech. badge was three stripes upside down surmounted by a brass Crown. Techies advanced by taking trade exams and serving a specified time between promotions. Conventional rank promotions, whilst still tradesmen, were more of a dead man's shoes system.
When the technical rank structure was abolished in the mid sixties (IIRC), the Ch. Tech. rank was placed between Sgt. and Flt. Sgt and the Crown was changed to a cloth four bladed prop. At the same time the J/T single upside down stripe was replaced by the same four bladed propellor.
Apologies for not using blatent as my laptop keeps correcting to blatant. Wouldn't want to upset the grimmer polis.