Port St Joe, FL
High-quality dog foods are nutritionally replete. This means that they contain all of the nutrients that dogs need.
Therefore, if you are feeding a high-quality food there is no need to mix things up.
However, as long as your dog doesn’t have a sensitive stomach there also is no harm in switching diets now and then. Some dogs will suffer from diarrhea or vomiting if their diet is changed suddenly. If your dog is one of those, then you should probably stick with just one type of food.
Some people are utterly fanatical about the subject of pet food. They are convinced that one type of food (a particular brand of food, or a particular home-made diet, or raw food, etc.) is absolutely, positively, the best food, and the only food that a pet should ever eat! In their minds, all other foods are basically poison.
In my opinion, there is no “best food” for dogs or cats. The high-quality brands are all fine. As long as you feed one (or several) of them, I expect your pet to thrive.