Non-binary views on health and depression

I used to have a binary view on health. You either have the beetus or you don't have the beetus. You are ill/a patient or not. It turned out, it is better to view these things on on a sliding scale. You really want your muscles to be highly sensitive to insulin as it both makes you not fat and not tired (removes at least one reason for tiredness: muscles refusing fuel). So you can function highly optimally here, or less optimally, or somewhat disfunctionally, and when your insulin sensitivity is really low you can call it insulin resistance and when it is really really low you can call it Type 2 Diabetes. Do you agree with such non-binary health attitudes about health in general?

If yes: what is that thing X that relates to (minor) depression the same way as insulin sensitivity to the beetus? What is highly optimal non-depressed functioning, what is the scale itself?

I propose: fun sensitivity / fun resistance. Highly fun sensitive people, like children or Zen masters, can find just about anything a reason to feel joy. A funny shaped tree leaf can make their day. Then on lower levels of the scale the brain refuses to feel happiness over these smaller jolts of fun because it is just a fucking leaf anyway so who cares and requires more stimulation to feel something. So "sex & drugs & rock and roll" it is. And in lower and lower levels of fun sensitivity, with more and more fun resistance you can minor depression then major depression. Does this sound plausible?

It seems then, we need a two-dimensional approach to be happy. We need a science of happiness which is largely about finding the ideal jolts of fun to input in our brain. And we need to make our brain sensitive to fun and not resist it. In the more extreme cases, depression treatment. In the less extreme cases? Meditation? Stoicism ? Opponent Process Theory ?

How to lower the fun sensitivity threshold? Does too much "sex and drugs and rock & roll" desensitise us to fun?