Ingredients aside, how important is protein content?

Looking at Wellness Indoor Health, the crude protein content is less than 30%. Comparing to Purnina One Indoor Hairball and Weight Control (which is probably what I would switch to had this allergy not occured) has 38%. Fat is higher in Wellness at 13% and Purina has 8.5%.

Blue Buffalo is higher with the protein at 34% but super high in fat at 18%. I also feel like they're biased as I did the "True Blue Test" against the Purina One and it said that Purina One doesn't have real meat as the first ingredient - which it does. So that tells me I can't believe the results. But I know it's grain free, so it has that going for it.
So I asked the vet, and she said the best protein content would be 100%. That rules out most dry food, because they put all that carbohydrate in so it will last a long time on the shelf, but cats need absolutely NONE of that, so essentially, you are paying for a high percentage stuff that at best, will just pass through, at worst, can cause allergic reactions, and make a kitty sick.

So wet food with very high protein would be best, other than cooking for your kitty of course.

Do not think, by the way, that cats "need" dry food to keep their teeth clean. Lots of people believe this, but in fact, the opposite is true. The carbohydrates in dry food are what stick to cats' teeth and cause problems.