I think the issue is that along with not having enough drivers, they also don't have enough driver trainers to accommodate the masses. Also, if you promote a driver to driver trainer then that creates a gap with one less driver to maintain services. Also, what then happens when you have trained your drivers and you are left with a surplus of driver trainers with no work?
Sounds like a very difficult issue to manage for any HR bod, so they have my complete sympathy.
It doesn't quite work like that, instructors continue to follow the roster pattern just as they did when they were drivers, if there is no trainee they drive the train themselves. When they have a trainee they still do the booked turn of duty except the trainee works the train under instruction.
That said you are right that there is only a certain number of DI's - it's not a job everyone wants or would be good at, they recently made up a number of suitable drivers to instructors and pretty much every Instructor has a trainee with them at the moment and the classrooms are full of trainees doing rules and routes. Basically the production line is at full capacity, I know how how it feels because I was in the pool myself, you've just got to grind it out your time will come
and yeah received no generic progress emails