If you are feeding cooked meat you will want to make sure you are supplementing it as cooking it will degrade the natural nutrients found in the meat. Also, keep in mind that protein isn't the only thing found in meat. It also consists of water, fat, etc, which confuses a lot of people (vets included). I know that the raw meat I feed my cats is under 20% protein, whereas most kibbles are 25-30% protein. Also, sweet potatoes are very sugary for a cat
Have the kidney issues gone away since cooking the meat? Also, you shouldn't have to worry about worms etc if you freeze your meat. Most people deworm a few times a year to make sure nothing sneaks in there, but a cat's digestive track is built to handle such issues when it is in a healthy state. If you are making your own food you would also want to include organs such as heart and liver.
Is there anything else like dehydration that could have contributed to the kidney issues? Vets often don't know a lot about raw feeding, and tend to blame it when it isn't necessarily the culprit. There is a great Facebook group called Cats Completely Raw and Proud that has some great info and may be able to help you as well.