I fed my last dog SD her whole life because we didn't know any better at the time. We just trusted the vet and all the marketing BS. Sure, she was fine on it in her youth but as she aged she developed bad allergies which we paid a lot of money to treat with pills when she would have been better off with a better food and no pills. But like most people we didn't know about how most dog foods are filled with corn, wheat and soy which are cheap fillers but also common dog allergens. We also didn't know that we needed to give her bones or brush her teeth and she ended up losing teeth in her old age. Then I went to work as a vet tech and realized most vets are like any other business. They are there to make money first and foremost. Out of 4 vets I worked under as a tech only one of them genuinely did it for love of the animals. The other 3 put profit first. And yes I had to sit there when the SD salesmen showed up and gave their little spiel and had to keep my mouth shut about all the health problems my last dog had as a result of their corn based crap that amounts to nothing more than Ol Roy walmart brand food at twice the price.
Now, I'm more informed so I brush my pups teeth at least once a week, give her bones, dental ropes and bully sticks to help clean her teeth too, clean her ears once a week, take her on daily walks and feed good quality food. I know raw food would be best but don't have the time or inclination to feed that way at the moment so I feed the best food with the least known allergens I can find knowing that it will save me $$$$ on vet bills later. I also know you can't buy good food at walmart or the local grocery store. You need to go to a pet supply store or tractor supply store. I've even seen good foods being sold at hardware stores but never at the local supermarket. So if all you've tried is what you can get at walmart or the grocery store then you haven't tried anything good, just one allergenic corn/wheat/soy based food after another. Feeding those kinds of foods to a dog is like having a kid with a peanut allergy, taking them to the doctor and spending good money on allergy meds and then feeding them a peanut butter & jelly sandwich for lunch which unfortunately is what happened to my last dog. Now it is so easy to be better informed to make better choices that will lead to a healthier dog and fewer vet bills in the long run.