There needs to be a balance between empowering people to make the lifestyle changes we can to improve our health by giving us the knowledge, encouragement, skills and resources to effectively make the changes we can ourselves...
But we also need to recognise that personal responsibility and self control didn't just happen to steeply decline in all age groups and ethnicities across the developed world 50 years ago. It isn't a personal failure, it's a public health crisis caused by a rapid change in the food environment.
There are things individuals who have the resources and can find the right information and have the existing health and ability to act upon it can do to improve their health.
But we are also very much part of a man made eco-system designed to keep us over consuming industrial produced edible substances aka ultra processed "food". Industry and Governments have been quite happy to push the blame back on consumers and tell them to take personal responsibility, to be "treat wise" etc rather than actually make sure that fresh nutritious foods are available to everyone.
A chunk of it is simply poverty - when people have more money they spend more of it on better quality food and have the equipment and time to prepare it.
Some of it is needing better regulations around the food industry and other environmental contaminants. There are obesogenic chemicals in the environment that encourage weight gain not just in humans and pets eating industrially produced food, but actually affecting wildlife and babies in the womb. Newborn babies haven't had a failure of personal responsibility. This isn't stuff that individuals can tackle alone, we need to work together as a society to make sure people have access to clean air and water and nutritious food.
It is so hard to make permanent lifestyle changes, loads of the ways people lose weight are not sustainable and they regain. People can be highly motivated and try so hard to lose weight, but our bodies pull out all the stops to prevent us from perceived "starving" by adjusting our hormones to make us move less and eat more, making food actually taste better.
WRT benefits, I think you could chop down the benefits bill much more humanely by reducing waiting times for healthcare and offering more support with lifestyle changes .e.g preventative healthcare and helping people manage their chronic conditions. If you did that on the health and social care side whilst also increasing access to further education, especially access type courses that people who have been out of work, education or training can use to try and build up confidence, skills and knowledge to retrain for jobs they could do, and work on creating more jobs that are flexible and open to remote applicants. Same effect of reducing spending on benefits, but with the human health and happiness benefits of people actually being healthier and more skilled.