I definitely agree that changing food options can do wonders for many hyper/allergic/itchy dogs. However, I've also seen dogs do just fine on the "evil" brands of food as well. It's a very individual thing.
In defense of the vet against holistic treatments, I can certainly understand his/her view. So many times we see animals in the vet field in absolutely terrible shape because people decided to try "holistic" methods first. I'm not totally against holistic medicine, but there also needs to be room for common sense. Too many people let their animals suffer through cancer or injuries trying a holistic method, when what they really need it medical attention and surgery. So often times we are left to deal with a case that could have been a simple case and now may not be able to be fixed. It's very frustrating, and very sad. That's why there are so many vets out there against many holistic treatments because when it comes down to it, many of them are Not a substitute for veterinary care and medicine.
There's also the issue that much of holistic medicine is not regulated at all, and we often see patients poisoned by their treatments. Not to say some things don't work, but it is sad enough to see a few cases that one easily becomes skeptical.
Many people go the raw option, but there are so many risks involved with that and I find many just don't educate themselves enough about it to feed a proper raw diet. Not to mention the salmonella risk to both the animal(s) and people in the household. The general rule of thumb at the hospital is if a dog is fed raw, it will be in at some point for malnutrition or salmonella. Too many people think you can just throw a bunch of cheap meats at a dog and that is ok. But in reality the diet needs to be so much more balanced than that. And you never really avoid the risk of salmonella, unless the meat is cooked.