The dogs I grew up with were all fed on raw meat and home cooking. They only ever went to the vet for a booster and rabies jab. ALL of them. I don't recall any sickness other than a serious adverse reaction to a snake bite once which was touch and go and very scary.
My dogs have had one thing after another over the years - skin complaints, digestive problems. I've had a torsion and various allergies. I've now got dogs on different diets. Two on complete foods and one home cooking (BARF - sort of! with my own variations)
lol - not sure what my point is exactly, but it's too much of a chew on to be faddish. It's what works for them and it's taken me years in one case to get where I am with her diet now. I find the one with the skin problems only does well on Nutro. Another won't eat Nutro at all. BARF is good but time consuming.
I only wish it was that simple to be able to find something and stick with it. I guess most people want what's best for their dogs and if they don't have any health problems but think that something else may be better anyway then I don't blame them for giving it a go!! Who knows - they may get superior results