Honestly, so long as the phos/calcium ratio is correct for growth, 1.2:1, the ALS food is fine to feed. You do want to make sure the calcium and phosphorus fall within this ratio as food above this (say 2:1.5) may cause issues with bone growth and development.
I will also add puppy food is just calorically dense/higher fat food, therefore you would feed double that of an ALS to a puppy, but this doesn't mean you are over feeding. Add to that, the feeding guidelines are just guidelines. Some dogs will need more, some less.
If your breeder is worth 2 cents, they would've put in a lot of time and research into the correct food that works best for their lines, so feeding what the breeder feeds is a sound decision.
I personally have fed Orijen 6 fish, an ALS food, to my lab mix and will be doing the same if I bring home a new retriever puppy this year.
