Breeding is complex and yes everyone will have their own opinion. So will people on the internet.
Breeders who’s goals are betterment of the breed are carefully selecting their breeding stock, importing new bloodlines and adding them to their program and constantly looking for dogs to add to their program without genetic ailments plaguing their breed. Those breeders are the ones that we need to help move away from the belief that pure breds are less healthy than mutts. For example Golden Retriever breeders are working to breed cancer out of their lines. Slowly they are accomplishing this. Nutrition plays a huge role in the health of any individual animal, but so does genetics.
Also as a breeder you have a responsibility to your breed to keep up with current research. That being said, the myth that “high protein” diets affect growth in large and giant breeds was debunked over 20 years ago with a set of excellent studies done on Danes. Dietary calcium and over nutrition, coupled with genetics are now recognized as the leading causes of DODs in growing large breeds. A growing puppy should never be put on a “senior” or adult maintenance diet. This was an old practice before companies developed quality foods geared towards large breed puppies. Now with all of the excellent foods available there is no excuse for having them on such an inappropriate diet.
