Protein level is largely unimportant, especially if it comes from meat sources. High protein from legumes like peas is questionable as a dog's digestive system is less equipped to utilize it than protein from meat. Some dogs don't do well on higher protein foods though and will have digestive issues which can manifest in chronic loose stools and diarrhea. Our pup has done exceptionally well on a food with 38% protein, so it really depends on the puppy.
The most important thing to look at when choosing a food for a GSD, or any large breed, puppy is calcium (and to a lesser extent the ratio of calcium to phosphorus) as has been stated already. A food that is high in ash will almost always be high in calcium as well as much of that ash content is a high concentration of bone in the meat meals used ... bone contains lots of calcium.
I certainly wouldn't consider 8% ash high, but I think anything over 10% ash is getting pretty close to being too high, especially for a large breed puppy. Earthborn Holistic does have a few grain-free formulas that would be appropriate for a GSD puppy, but Primitive Natural is not one of them.