First things first, If you do not trust the recommendations of your vet it may be time for a new one.
This is what is know about nutrional effect on bone growth etc and development of large breed puppies high protein is not a problem, high fat content is not a problem, nor is high carbohydrates. What is a problem is to many calories. The easiest way to control calories is to feed less. Rather than switching to a poorer quality food. Switching from a puppy formula to adult formula will also reduce the calories per cup of any given brand of dog food.
On could always switch to Dick Van Patton's Natural balance and get a highly rated pet food that is both lower in portein and fat and higher in carb than Pruina Dog Chow. This is to say, much about dog food pricing has nothing to do with actual nutrition and everything to do with marketing. There have been a lot more dog successfuly fed on purina dog chow than those high priced super premium brands.
There is no evidence that diet plays a role in pano so changing the feeding regimin is not likely to change the outcome nor if it were done earlier prevent the problem in the first place. There are many theories on the cause but in the end when they are put to the test of scientific scrutney the don't hold water.
On the filp side changing the diet is unlike to cause any harm either so as most physician are wanten to do nothing the change of diet is often trecommend
Panosteitis in Young Dogs
Canine panosteitis
Growing Pains: Successfully Raising the Large Breed Puppy
As for specifics niether my vet nor ortho specialist recommend a diet change in any dog diagnosed with pano.