I don't know what period Eric is referring to.
I suspect he's talking about the 1990s. Frontline First/Options for Change and the peace dividend meant promotions from Cpl to Sgt were few and far between.
Recruits are turning upto a frontline squadron knowing nothing, without being taught any flight line operations. So frontline squadrons are now expected to teach their new arrivals what was originally taught at Cosford.
Does Line Training at Cosford not exist anymore? I taught there in the early 00s and I always thought it was outdated and badly focussed even then. All we produced was people who could carry out a 4-man servicing on a 1950s training aircraft. We had a visit from some sqn training cells, who told us that mechs arriving on the sqns insisted they hadn't received the training that they absolutely had. The trainers were shocked to see all the training objectives that were printed on the back of the training certificates! Also, the AMMs (at the time) were not being used to their fullest extent when they got to the sqns. Most were just used as lineys with no trade experience being given, even though the Mechs and AVs had first sig in both trades.