I have read the Hovan slow growth plan, and I do not agree. Puppies grow incredibly fast and need nutrition--as mylissyk states, not just for bones, but for their their whole body. Puppies are growing brain cells, organs, as well as bone and muscle. It is imperative that they receive adequate nutrition to support this growth.
Moreover, genetics, more than any other factor, will determine how quickly your dog will grow, and what size he ends up being when he is mature. Genetics are going to determine whether your dog ends up with hip dysplasia. After all, HD is a genetic defect--which is why breeders do X-rays prior to breeding.
Blue Buffalo recommends 1.5 to 3 cups per day for a pup under three months that will be 50 to 100 pounds at maturity.
You are feeding half of the minimum recommended amount. I encourage you to increase Zeus' daily food to at least 1.5 cups per day. BB recommends feeding 3 times per day. That would be .5 cups per feeding.
Also, I would not worry so much about the growth chart. Does he appear overweight? Each puppy will grow at his own rate. Give him the nutrition he needs.