The fallacy in that argument is that if these people all had the most perfect diets they wouldn't be sick in the first place.
What? This is hogwash. How can you possibly claim this as any sort of fact?
It's absolutely a fact. Diet has a profound effect on the human condition. A good diet is the most important thing you can do for yourself. A good diet is nearly impossible to get these days, what with pesticides on vegetables and antibiotics in meat and eggs, but possible if one is willing to spend the money. Organic fruit and hormone and antibiotic-free food from places like Whole Foods are good. But even then, there are complex vitamins, flavanoids, and enzymes are so fragile that they start coming apart and degrading within minutes of being plucked from the stem, many of which are impossible to synthesize in pill or liquid form.
The absolute best diet is all but impossible for most people today, but it is to eat as naturally has humanly possible: how our ancestors did it. Meat must be fresh. Fruit and vegetables must be eaten from the vine, from the ground, and full of dirt and covered in important soil-based organisms which are also symbiotic to animals. People self-identifying themselves as "healthy" who have done this have reported feeling full of life, clarity, and an overall sense of being in prime health.
There are many reports of people on Curezone who have cured their Type II Diabetes, a condition considered incurable in medicine, by going on an entirely raw diet. There are reports of people who have resolved their Chrons Disease, another incurable condition, through soil-based organisms.
The benefits of megadosing Vitamin C is great and all, but no one should have gotten to that state to need that in the first place. Our immune system was evolved over billions of years to live in a healthy state in symbiosis with a primitive style of life in tune with nature. The closer we can get to that, the healthier we will be.