Your point is extremely important. There are few diets that have shown real affects long term on quality of life and life extension. One is calorie restriction, the other is a version of the Mediterranean diet which is along the lines you are describing. This variant (also with things like fasting, exercise, brain game training, sleep, and red wine) I refer to is actually the only pathological evidence that I am aware of that showed a reversal of dementia symptoms. One of the most remarkable studies I have seen in the decades when I was involved in science and drug discovery.
Genetics. Some people smoke cigarettes for a couple of years and get lung cancer while others for 60 years and don’t. The effect of genes on diet and health are much stronger than diet. Genetics sets your base level and diet then can influence it. Exercise and sleep are also important factors in varying the base health you have through genetics. You can really influence your genetics with the right regimen, but the data on what that is exactly is not defined. Unfortunately, all the diet fads muddy the real data further, like just don’t eat carbs! All non-carbs are not created equal, in taste and health affects.