It is true that there is such a thing as “energy balance”, but the crucial thing that is left out of the equation is the nature of the person’s diet, which determines what their weight will be once they reach energy balance.
The numbers above are imaginary, they are only there to illustrate the way different “all you can eat” diets lead to different weights.
I have tried various diets throughout the years. A strict keto (ketogenic) diet reduces my motivation to work, even though it is great for blood sugar control. Currently I follow somewhat of a Mediterranean/low-carb diet. I avoid bread, rice, potatoes and all other foods that contain significant amounts of simple carbohydrates, since these foods make blood sugar management impossible regardless of how supposedly healthy some of them are. I also avoid eating more than 50 calories of fruit per day, as I always get neuropathy in my toes and fingertips the next day if I do so.