The diet your vet recommended to you is not a complete diet! Please people don't listen to vets about nutrition unless they have undergone extra schooling to become nutritionists. Yes dogs are carnivorous, but that includes more then just meat. Bones, intestines, organs.

Second, Dogs cannot digest cooked meat. Raw meat contains the enzymes that they need to properly digest things. Cooking meat allows for the digestive process to slow allowing for bacteria to multiply in the intestines and gives the possibility for food poisoning.

While it is true that variety is good, you can get proper nutrients in kibble dog food, its more the moisture that you should be concerned about. When a wild dog kills and eats something 75% of that is moisture, so a few pounds are needed. Dogs do not drink this much water and are more prone to dehydration then poor nutrition.

Upset stomach is common among dogs because there are wheat, soy and corn in their food and they ARE allergic to these, not because they need more variety. When switching a dogs food you should allow 3 weeks for the full transition.

Your analogy with the steak's is a poor choice, as the cut of meat and its preparation is what your paying for, not the amount of protein, much like the difference between quality foods like orijen and crap foods like petigree.