It's a known fact that most/all of the research on dog food, is done by dog food companies. Veterinarians while in school, spend very little time studying nutrition. If the only research available is by a dog food company. Then without a doubt, that's what they are given to study.
My thoughts on DMC and grain free.
There has not been a study large enough, or in depth enough. To say grain-free causes DMC, or does not. Do companies have a lot at stake on this study? Absolutely. Some with a lot to gain, and some with a lot to lose.
Just because DMC is showing up in breeds, that it hasn't in the past. Might only mean, more owners are doing extensive testing. I feel the same way about some cancer in dogs.
It's a dog-eat-dog world, and hard to know who to trust.
digital world information can be a minefield, my family has had all manner of dogs in my 5+ decades on this planet, from terriers to labs to whippets and lurchers, pointers, setters alscatians,,etc etc etc, none have shown any ill effects from "scraps off the table" along with their food.
As far back as I can remember, I've always been around pointing dogs. During the hunting season, and very cold weather. My grandfather would have my grandmother, make cornbread for their dogs. He said, it helped keep weight on them.
It must have, because his dogs always looked good.
I agree dogs don't digest whole corn.
They do digest corn meal.
I'm a do what works for your dog, type person.
If you want a feed grain-free, feed grain-free.
If your dogs doing great on the food with grain in it. There is no reason to change.