I'm sure it's true that people and animals do better on a raw diet.
I don't like hearing people mentioning Pottenger, however. What he did was very abusive to a lot of animals. Also, the cooked diet he fed half the cats was an absurdly deficient diet. My understanding is that he gave them meat scrapes and milk, while the diet of the raw fed cats included bone. Cats cannot digest milk, and they cannot utilize the calcium in milk. It's no wonder that the cooked group was so unhealthy.
A better experiment would be to feed one group of cats a raw diet that includes bone meal for minerals, and the other group the exact same diet, cooked instead of raw. The result would not be nearly so dramatic.