Rotters
I am afraid it is a fundamental error to think that the RAF treats each person on their merits. Like all commercial employers processing X,000 applicants per year, they have to work to a set of general outline assumptions and on the basis of past experience. Only when you have proved your potential to them can they afford to focus on you as an individual. Obviously, as you manage to clear the hurdles of the initial application, basic training and advanced training, the strength of the individual to negotiate these deals increases, because their value to the Service has increased. Sadly at OASC, your bargaining strength is pretty paltry, therefore those that meet the sausage machine standards are most likely to be taken on as representing the minimum training risk.
But remember, the RAF does have a quota for graduates/non-graduates - is it 70/30 now? not sure, I last dealt with it about 4 years ago. But they do not exclude the non-graduate entrant, far from it, they appreciate the diversity that the non-graduate experience and talents can bring. However, the training stats speak for themselves, graduates have a better pass rate. What the stats don't show is what the various success rates for non-graduates is, based on their academic or real world experience, probably because it would be very difficult to ennumerate.
There are two reasons for paying someone with a degree in Golf Course Management more as a graduate entrant to the RAF. Firstly, statistically that person is less of a training risk than a non gradute (see my comments before re academic attainment - the subject is irrelevant, it's the learning skills that matter)- the RAF are paying for the better candidate - simple economics.
Second reason, again simple market economics, graduates expect a certain level of income (see the OPs comments), while the RAF can try to wrinkle a little flexibility out of those that join for the vocation etc, it has to attract the quality of candidate that it wants, that means offering graduates a market salary. The RAF can get away with paying non-graduates less because these people do not have the claim to the 'graduate salary' (or if they think they do - tough!) but they still (on the basis of selection) have the vocation, desire etc that make them worth the training risk.
It's economics - managing the supply and demand, and the training risk. Of course there are always going to people that defy the stats, and if you have a good recruitment system, as the RAF has, then these people will be spotted and will reach their potential. However, for the majority, it's a procedure, a system and the individual has no merit in that system until they have proved their value.