Well, IMHO, thats not true at all. You can buy hills in vet, and its actually a poor quality of food for cats, especially the urinary ones. They are so full of grains/fillers and cats dont eat vegies.
You can most certainly buy quality, even the best in your store or online for convenience. For dogs there are so many types, and it depends on the age of the animal what/which you choose. Also the size of the dog.
Some large dogs grow so quickly, you need to get foods with extra calcium, or add it at each feeding.
Read the ingredients, just like you would when choosing your own foods
. Dogs love grains and vegies, they just need to be in the correct percentage. You can make your own dog/cat foods too, which is a lot of fun, for a while.
I did that for years. I had a dobie, a grey, and a chihuahua. I made it once a week, purchased the vit powder online. Its when i was a true vegan, and I turned all dogs/cats to vegans with me. Lol. The cats loved their food, although its very difficult to find non-meat sources for their vits.
Good-luck on your new pup!