Controlling calorie intake is hardly a magic bullet. That's like saying exercise is the magic bullet for gaining muscle or studying is a magic bullet for passing exams.

A magic bullet in this case would be something that allowed weight reduction with no restriction of calories. From experience, restricting calories long-term is very difficult.

Dieting isn't a magic bullet you fool, it's long, hard and worth it.

Just being hard, or even applicable in some cases, doesn't make it less of a magic bullet when someone suggests it's applicable to a broad problem.