Yes, fitter and healthier is possible — those are relative terms. But there are plenty of reasons that for some people, low weight is easy, and for some, it is not possible. People who are overweight or obese typically hear everything you have written and more, over and over, by well meaning but ignorant people and doctors.
Do you really think it is ignorance that cause all stubborn obesity? Or refusal to exercise? Or refusal to eat right? If so, you eed to study the issue better.
Also, your dismissal of dieting is incorrect. Reducing caloric intake is important if one is taking in too many calories. Dieting does *not* cause weight gain, unless done incorrectly. Sure, fad diets rarely work. But neither do medically designed and supervised diets, and diet and exercise programs. Look at the stats: 95% regain the weight.
When you say “Being accountable for our…” — you are being dismissive and arrogant.