Birds that are from breeders, bred to the breed standard and not for a mass amount of eggs are much bigger, meatier birds and have a different feather structure than the same "breed" sold by hatcheries. The breeder birds needs and can use the extra protein for proper growth, size, and feather...
If you got them from a hatchery 18% protein if fine for the Orps, Dominique and Rocks.
If the Orps, Dominique and Rocks are from a breeder 18% protein would be a minimum amount I would feed. (I would feed closer to a 20 to 22% protein if they are from a breeder)
Chris