Hi Pete, I'm fully familiar with all the traditional aversive methods, having used them very successfully for the best part of 40 years.

I'm now experimenting with positive reinforcement methods because they are an interesting challenge, & I've grown tired of imposing traditional methods on my dogs. I generally shoot on my own & always over my own dogs so am no longer influenced by peer pressure or convention, & so am in a better position than most to grapple with the complex problems that come with training using 'positives'. If you like, It's an acedemic process for me. I've also moved on from the bog standard clicker type training & am now more interested in developing environmental training - where I manipulate behaviours but the dog doesn't realise it is being trained. I no longer do any formal obedience training in the accepted sense. Many people believe that the use of edible rewards is easy, at least in the early stages, but it is fraught with problems for the inexperienced. As you have seen from the number of problem dogs you are asked to sort out. The biggest problem is in distraction proofing the behaviours. A lot of pro trainers in the States do all their puppy training using positives, but then incorporate low level e-collar use to get around the problem of distractions. But you are right, it's not just about edible rewards, but also praise & retrieves & being allowed to hunt on as a reward for doing a behaviour correctly. It's just that edible rewards are often more accessible to the dog than most other things.
I'm also aware of how many pups a pro trainer in this country gets through each year in their selection process. It's interesting you mention David Lisssett. A friend of a friend has just got an 8 month old pup from him, from his own breeding, at a knock down price because he considered it too soft. And he wanted it to go to a pet home, even though it would have made the grade as a shooting dog. There were 2 dogs sold on like this from the same litter.

I'll be seeing it later this summer so can't wait to see what its like.
Naj