Large breed puppy food is essential for the proper growth of a large breed puppy.
I also have a large breed puppy (GSD) and she is fed human grade puppy food. The only foods that contain garbage are the usual garbage dog food sold in supermarkets. For proper dog food, one must go to a store that specializes in animals, not people. If you feed your puppy garbage food, yes, you will experience uneven growth and possible health risks down the road.
Continue to feed your large breed puppy the food you're using, as their bodies need the protien to keep up with the bone growth. Monitor the amount of food you feed and adjust it accordingly so that the pup doesn't gain too much weight when it starts a growth spurt again, and it will if it's like my pup. She too went through a stage where it looked like she had reached her final size...but alas, she's growing again. If the pup is growing very slowly, you could mix in some adult food with the puppy food to slow the protien buildup. I also look at my container of dog food wondering why in heck I bought so much, then....4 cups of food a day later, I remember.