Exercise and diet have positive health effects other than losing weight. Many people with normal weight according to BMI still have an unhealthy body fat percentage. That said, if this drug can keep its promise it will have an enormous positive effect on public health.
If you’re regularly doing something unhealthy (like smoking or eating lead paint chips), stopping that is both good for you and a shortcut.
My understanding is that the way the drug works is by improving your diet.