It's the carbs that concern our vet about dry food, too, particularly for Siamese mixes: she recommends high-protein, low-carb wet diets for all cats but especially Siamese because they tend to develop digestive problems. Carby ingredients just aren't very digestible for cats to begin with -- it's that carnivore thing! -- and we've definitely seen that on a small scale with our cat who vomits if she eats foods with potato. We adopted her at ten months old and she already had the problem.There are actually only 2 dry foods on the market that are low in carbs: Ziwipeak and Dr. Elsey. Unless you’re feeding one of these the food is high in carbs.
I definitely understand @DanielBunbury's concerns about certain ingredients in canned wet foods, though: there are so many ingredients that I refuse to feed or prefer not to feed that it's hard to find a rotation of foods to feed just one canned meal a day! Just refusing carrageenan, potato, and peas drastically reduces the number of foods available. Adding in menadione cuts more, and so on and so forth. Though I'd much rather not feed foods with gums, they're in some of the canned foods we feed: I think they're likely to be less harmful than the carby stuff in dry food that cats just don't digest and metabolize well. As I see it, the best I can do is be aware of the risks of various ingredients, know what adverse reactions to watch for, and then make changes as necessary.