Obesity is a problem of modernity and specific cultures made up of people who didn't used to be obese generations ago. Are the populations around the world in which people aren't generally obese just filled with a large subset of the population constantly starving...or we agree that no such large subset is simply destined to obesity.
If we agree on this, then your argument isn't that people are destined to obesity, but rather that once they're obese, they have patterns of behavior that are extremely hard to break over a long term basis. That isn't the same as saying that weight loss is a futile endeavor, it's just saying that people who are obese are very often going to fail to stick to the patterns of behavior that resulted in weight loss.
My argument is that in 2022, the medical advise and consultation of “diet and weight loss is the solution to obesity” is not true on a population level. We now have other tools to address obesity that are both pharmacological (GLP-1/GIP acting) or surgical (bariatric surgery). We should stop admonishing patients for not following treatment guidance (eat less, exercise) and instead provide them with solutions that actually work reliably. I have nothing to add to the causes of obesity, and eating properly and maintaining a high level of activity are clearly good at preventing people who have never been obese from becoming obese.
If we agree on this, then your argument isn't that people are destined to obesity, but rather that once they're obese, they have patterns of behavior that are extremely hard to break over a long term basis. That isn't the same as saying that weight loss is a futile endeavor, it's just saying that people who are obese are very often going to fail to stick to the patterns of behavior that resulted in weight loss.