Hi Rachael,
Sorry for the slow reply, I was on a road trip this past weekend.
I feel your frustration, I’ve been there for sure. The first advice I got from a vet about puppy food was don’t give it to a Great Dane. The reason is that Danes need to grow slowly and puppy food is designed for rapidly growing bodies. However that advice was given a long time ago and I don’t know that giant breed (or large breed) puppy food was a thing then. The grain inclusive is because grain-free foods tend to have lots of pea-protein and other legumes which have been tied to heart disease in some breeds. Just so you know it isn’t the grain that is important it is the lack of legume products.
We used Holistic Select for years and I believe they have a giant breed puppy formula. We were recently trying Eagle Pack for Martok but after a few bags his poop was getting soft so I took him off it. Believe it or not what is working best for Martok, who is 4 years old, is Costco Lamb and Rice. It is what the Great Dane rescue we got him from feeds all their dogs. I haven’t used any of the brands you mentioned except that Canidae used to make California Natural which was the only food that agreed with our first Dane, Selar. She had a very sensitive stomach and needed a bland, simple formula.
The food grade system I have in the article will give you an idea of what ingredients are good and bad. You want a couple of specific meats to be the first 3 ingredients.
I don’t think you need to worry so much about it being specifically for puppies, I believe some of that is just marketing. There really are a lot of quality brands now. We have always gone with the advice that low fat and low protein are best, though I don’t know how much science is behind that. Stick with ones made for large or giant breeds.
What I have learned from all our Danes is that each one is different and a food that is liked and seems to agree with one doesn’t work for another. I know the doesn’t help much but I guess that is why there are so many types of food out there.