I agree. Many trainers use to much fear to teach a dog. I dislike most online dog trainers i have the few i like and watch.ANY dog? sounds like you should be a professional trainer then - or are you?
Incidentally, I've watched numerous professional dog trainers train retrievers for field trails for many years - they also could get ANY dog to retrieve ANY duck by instilling enough fear and inflicting enough pain. I watched too many dogs yell and yipe when being zapped. No thanks. One size does not fit all. It depends on what the individual is comfortable with and how much time they have to invest in training given the responsibilities of their life.
I find e collars ok if used right. Oir pups are properly conditioned and its only used for offleash time. Which i normally dont even use it then.
You cant always teach every dog especially a dog thats already has the drive set.
I wouldnt ever try to take the drive out of my retriever even though he is scared of guns.
But thats my opinion to and i dont want to start anything