Some very good points made. There is, across a broad range of professions or hobbies where those that have been doing it for a long time know best, but, new blood brings new ideas, and without new ideas, things will stagnate, and we'll get stuck in a rut.
I still think, though, that it is important that the people who provide the training are able to impart their knowledge in a meaningful manner, and the only milestone that we have to go by are professional teachers - be that educational, or RAF QFIs - no I'm not saying FIs are unprofessional, just that 99% have an alterior motive which is to get a job with an airline.
The people who do the teaching should be able to effectively impart knowledge to all sorts of differing personalities. In order to do this, they have to be able to identify how to teach someone. Some will have a natural ability to do this, others will not, therefore some sort of formal training in teaching could help improve the training experience for students. I guess the problem is funding as I am sure already overburdened fledgling airline pilots would not want to have to fork out further - maybe an extra tenner on the cost of a PPL would help - if you can afford 6 grand plus to get the thing in the first place you could afford another 400 quid I'm sure - just so long as that money goes towards helping FIs become better teachers with some sort of vocational training.