Civvy flying mil aircraft
As a former Viking instructor, I must say you are badly informed on the VGS side, and saying we just "rock up" is offensive in the least.
On completion of your scholarship as a cadet, you have the option to apply for Advanced Glider Training, which shows advanced (surprise) techniques and 5 solos. You have the option to come back as junior staff, which includes what could be called "on the job training."
The end result is a home-grown core of staff members who only become instructors upon completion of courses with Central Glider Squadron at RAFC Cranwell and RAF Syerston. The only people who might have a shorter path to the CGS are those with previous flying experience.
As for FRADU, you have no chance without previous fast jet experience. As for the AEFs, if you aren't in the RAF(VR) or a service pilot or in a UAS already, forget it.