It is probably more than half the story. Health span is strongly correlated to life span, although not completely. The median "health span gap" is about 10 years, and has widened by roughly one year over the past 20 years. However, this is probably just due to an aging population and not necessarily from any factors you can control fully.
I wouldn't be surprised if "health span" (although defining it is difficult) exactly mirrors the inheritability pattern of mortality.
It depends on the definition, if you're even just 20kg overweight you're living a wildly different life than you'd have if you were fit, you're closing so many doors by default and making a bunch of things much harder than they should be, But you're still considered "healthy" here
This is such an underappreciated fact. Lots of people think 20kgs overweight is normal, they'll call you skinny and tell you to eat more if you're a healthy weight. An adult man of average height should probably not weigh more than 80kg. It could be okay if you're very muscular but most likely you'd be better off losing a few kilos. And being extremely muscular to the point where your BMI says overweight isn't exactly good for your health either. Though probably better than just being fat.
I wouldn't be surprised if "health span" (although defining it is difficult) exactly mirrors the inheritability pattern of mortality.