Watch a person take a dog for a walk. Is the dog walking the person or is the person walking the dog? Surely you can tell. The amount and intensity of the exercise that is needed or required for each is different and needs to be accommodated. The good behavior of a dog walking obediently on the left side of the person may look impressive and let the whole world watching be assured of their safety but is the dog getting enough physical activity and pleasant diversion.
How far away is the dog walking and in what direction? How distracted is the dog and for how long? Every living being needs exercise but the diversions of each is varied. The person may admire the scenery while the dog may be intensely interested in the scent on the next pole. There are two different thoughts here that can be considered and accommodated.
Depriving this faithful animal of its normal life is not the result of being the Master. The Master is the Master because he knows how to care. This knowledge is not only caring for the dog in the way dogs need to be cared for but to care for the Master also. First and foremost be the Master of yourself before you take on additional responsibilities of an entirely distinct species. It is a fact that humans and dogs are both living beings but they do require species specific attention.
Considering the reason why you have a dog is such a valuable thought that I present it as a constant. Always think of this.
If the person is actually the Master then the dog is being cared for by the person. That does not mean that the person is not benefiting. Caring for oneself is the essence of caring for your dog.