That makes sense, the sad truth however is that most vets are poorly educated when it actually comes to pet nutrition. Most veterinary schools don’t put a large emphasis on it, so the doctors rely largely on what they hear from food manufacturing reps.
Overall, the incidence of food related allergies in dogs is actually very low. Of all allergy cases in dogs, only 10-20% are caused by food, and of those, only about 10% of those cases are related to corn. Basically what this means is that in only 1 or 2% of dogs with allergies, the cause will be corn. Basically only 1 out of every 100 dogs with allergies will be allergic to corn. Factor in that only roughly 1 out of 10 dogs has allergy issues, and we are now saying that only 1 out of every 1000 dogs has a corn allergy.
As for boosting protein levels, there is no evidence that this is true. As far as the body is concerned, protein is protein whether it comes from a meat source or a vegetable source. Protein quality is determined by two factors: 1. Amino Acid profile, and 2. digestibility.
Corn, believe it or not, happens to be a good source of protein, it has sufficient levels of nearly every essential amino acid, and corn gluten meal in particular is comprised of 67% protein, which is actually higher than most meat meals, and only slightly lower than byproduct meal (which has a very high protein density). As for digestibility, corn meal is 87% digestible, which is more digestible than most meat protein sources.
If you are interested in where I got my information, there are many research articles on the internet where you can find all of this, this article in particular could be very helpful: https://www.vetlearn.com/_preview?_cms.fe.previewId=9955a990-1205-11e1-a602-0050568d3693
