General health goes beyond body fat percentage.
It's possible to have two people of the same weight, strength and bodyfat, but one is unfit with adult onset diabetes and risk of heart disease, and the other is fit with no health problems or risks.
Just think of the classic Italian mamma, obese by Anglo standards - yet she is healthier and lives longer than the Anglo woman with less body fat.
Health isn't measured by the size of someone's bum. It's measured by a combination of things. Doesn't mean body fat doesn't matter, simply that it's only part of general health, and not even the most important part. The most significant contributor to longevity is cardiovascular fitness, and after that social connections.
Obesity is usually an effect of poor overall health, rather than a cause of it. That is, the person has a poor diet and little physical activity, and then becomes obese. Of course the effect then contributes to the cause: because they're heavy, they avoid physical activity more, and have to entertain themselves while not moving, for example by eating more. But the prime causes are diet and inactivity; obesity is an effect.