This is so true! A vet friend told me years ago that there's really no training in vet school on nutrition, and that the foods they recommend like Hill and Science diet are due to the marketing those companies do to vets. My holistic vet has a more reasonable approach about food but pushes raw, which I can't feed, so it's a real dilemma for the average dog owner.
The only answer is to do your own research and make the best decision you can for your dog. I spent several days finding my current food after a nutritionist told me to avoid foods with the latest fad additive (that many think is responsible for the DCM surge) of peas, pea products, lentils and potatoes. That made sense to me, since dogs are not meant to eat them as one of their main protein sources. But it was hard to find anything that didn't have those ingredients near the top of the list!