My dad used to feed #9 to his beagles. I don't know if the quality was any better 30-40 years ago, but the dogs did ok. It probably helped that he would also feed them cooked meat when available (he hunted with them, so if he got rabbits or other animals, they usually were cooked and given to the dogs except for some of the deer meat), leftovers from dinner, and/or stuff from the refrigerator that would have otherwise gone in the garbage. Basically they were canine garbage disposals.
Back then, most processed dog food was horse meat. Many dogs grew up being garbage disposals as you said, and things like dog food were just supplemental extras thrown in when there weren't enough scraps. A lot of dogs didn't have the luxury of having supplemental food. They ate scraps or went out and hunted a bit. Dogs survived like this for ages and did just fine. Then the enterprising James Spratt came along and changed history for pets.
If you've never read the history of dog food, you'd probably find it interesting. Most all tell it the same way, but some have extra facts that others don't.
http://www.neatorama.com/pet/2013/05/20/Kibble-Me-This-The-History-of-Dog-Food/http://test.luckydogcuisine.com/2015/05/16/history-of-dog-food/But heaven forbid that anyone figure out that dogs could do just fine living the way they did since they became companions. That would kill someone's bottom line.
Besides, who cares if dogs live as long as they did in my parents' time when 15 year old dogs were a norm? That might mess with the bottom line of puppy mills and pet stores that sell those puppies.
It seems that the only ones not worried about bottom lines are those of us that love these animals--beyond belief to some.
