Not so much a sore subject as misinformation, advertising and internet postings taken as fact.
You have given a great example of finding a food type that works for your dog and trying to stick with it. There is obviously a GI issue that has been addresses successfully with diet and you have a happy, healthy dog.
This situation points out a difficulty with getting information (especially medical) over the internet. None of us have the history and medical information that you and your vet have and run the danger of giving inappropriate responses.