How have you determined that? Sure there may be overstaffing, but with the movement with taffs well depot many of those extra staff may move there. Also, my friend said theres many senior drivers who are close to retirement but they have to give a year notice, so there may be movement with that also. Also just being optimistic, TfW have put another trainee driver post for Chester, which I think shows growth and is overall positive. When my friend got in as a trainee, he said they had new courses starting every two weeks and that ran for like a year - of course thats not the case now but 6 courses shouldn't be out of reach.
We have until 2028 which is plenty of time, I pray that full allocation of time isn't used.