High protein is fine for healthy cats. Calories are supplied by carbs, protein and fat. This is a low carb food...in order to reduce the carbs, the protein levels must be increased. Also, keep in mind that comparing the minimum percentages in the guaranteed analysis is not accurate because of the calorie differences amoung various brands.
According to the AAFCO nutrient profiles, the minimum amount of protein should be no less than 26% for adult maintenance and no less than 30% for growth and reproduction assuming an energy density of 4 kcal/g ME. Foods with greater than 4.5 kcal/g ME will required higher levels of protein.