Our puppy's foster was using some Walmart offbrand food... you bet I switched, lol. My older dog was on Iam's. Didn't last long either. He was a rescue too though, so I wouldn't expect them to spend more for quality food.
My dog was on a pretty decent food at his foster, so I didn't switch him. It was a Costco brand puppy food which rated well on Dogfoodadvisor, and he was doing good on it. I only switched him when he was 1 year old to an adult food.
I did, but only because the specific bag of food she was feeding was difficult to get here - I would have had to order it in. She owns a business and was able to bring it in, but after having issues herself getting it in she has now switched to a different brand. I kept him on the same protein, fish, but switched from Wellness to Acana. (She had given me a brand new bag when I picked him up, so I had some time to make the switch.)