I haven't looked into it, but I strongly suspect you're right on the mark with that last remark. 

I think a great deal of the benefits that come from the carnivore diet aren't actually from cutting out non-meat food, but rather are from cutting out all the highly processed cereals and grains.

Fruit and vegetables are good for you, so is meat, and natural un-processed carbs. It's the artificial stuff that contains a billion ingredients that's the problem.

AskSN

How can we combat the obesity epidemic?

Aardvark

There's also a problem in the opposite direction where people think you're supposed to eat no fruits or vegetables. Too many people are making money off of making bold unsubstantiated claims in the fitness and nutrition industry. 

While i don't think there's anything particularly wrong with things like the carnivore diet, I'd argue that any balanced diet full of mostly single ingredient foods is going to be fine. 