Does dog food really matter so much?

I have been told my uncle (who is a professional dog breeder) to feed your dog with as much natural, preservative and chemical free food as you can. He told me you should treat your dogs diet like a healthy diet you would advise a human to eat.
The main things are checking all the ingredients in the store bought food and to look for human grade ingredients. The best thing would be to prepare food at home and using a ratio of 40% protein, 30% grains, 30% vegetables and of course added oils.

Your dog will be much healthier, happier and long lived