It’s basically impossible to make dry cat food hold together in pellets with significant carbohydrate content. And this cat refuses to eat wet food (or any food other than dry cat food).
The line between allergy and intolerance is very fuzzy. The inflammation resulting from “intolerance” is caused by many of the same immune system cells and molecules that are responsible for a direct allergic reaction. And the inflammation in the digestive tract is what results in the digestive problems and in severe cases, in serious nutritional deficiency due to the inability of the inflamed digestive tract to absorb nutrients from food. The inflammation can be caused either by a direct allergic response to certain substances or by the failure to digest certain substances which then reach parts of the digestive tract that weren’t designed to handle them.
Allergy is an immune response. Intolerance is a digestive system response. Symptoms may be similar but the are different things.
http://www.webmd.com/allergies/foods-allergy-intolerance
Interesting fact I learned back when I worked for a Vet. Cats often will only eat the shape of food they are used to. It’s the reason for all of the funny shaped cat foods, as opposed to dog foods which tend to all be the same shape (and dogs could generally care less, they will eat anything). Still, cats’ natural food is not potatoes or grains.