I will reiterate some things and relay some new things. Cats are true carnivores. They should NOT eat any grain, period. They also do not need vegetables or fruit.
Also, I'm going to have to disagree with the idea that vets routinely use foods that do not work or mask symptoms. Having worked in the field for over 12 years, this has not been my experience. We consistently see very good results from prescription diets. I'd love to see any studies showing that feeding low-grain or raw diets improves rates of kidney disease, hypothyroidism, and cancer, though, since you've asserted that that is the case. Maybe I just haven't been made aware of the relevant science.