The only case where a dog should be permanently on a soy based food is if they have EXTREME allergies to every other protein. Which is incredibly rare and will probably be a life long struggle for u and him if that is the case. Diets like the one he’s on are usually given for elimination diets to narrow down ingredients the dog is sensitive to. I’ve have seen ppl who feed chicken based diets and the dogs are horribly allergic to chicken but when switched to a fresh or raw food diet they don’t have the reaction anymore. If you’re interested in adopting the dog I would see if the rescue (or your vet) can refer u to a vet nutritionalist whom can make u up a proper balanced diet using fresh foods that wouldn’t flare up his allergies.
