Roly old chum, this was always a favourite topic of yours when we knew each other in a previous existence. The wise heads (and I don't mean me) told you then that it was bolleaux and it still is. As even some of your ex-Nimrod colleagues have also stated.
If you look at the Accident Report following the Hercules which was lost in Scotland, you will find some strong views from the AOC of the time about 'on the job osmotic training' - the sort of thing which ArtField and I rail about. "Let's spread the training to the squadrons so that some Golden Child can get a career-enhancing instructional tick" seems to be a popular, and highly dangerous trend. Proper, independently commanded training organisations with a formal, disciplined framework is the ONLY safe way of doing things - not training conducted by on-squadron self-appointed, unqualified 'experts' who happen to be the boss's blue-eyed boys...
On the Vickers FunBus, we didn't train co-pilots, we trained First pilots. That they sat in the RHS is of utterly no consequence - the good ones did well and many have since been promoted.
The reason that most of the squirearchy at the Covert Oxonian Aerodrome is of a single-winged flavour is that their pilot peers have mostly legged it to the airlines due to dissatisfaction with the way things have gone. Whereas navigators have nosuch option - without it costing them £40K-ish to re-train.