What if someone eats the same but creates the caloric deficit through increased exercise? Will they lose weight?
Just like OP you want to simplify things as calories in/calories out while entirely ignoring calories out.
Losing weight is not healthy in and of itself, even in obese people, however, losing weight can be a byproduct of making healthy dietary and lifestyle changes.
Calories is just a unit of measurement of metabolic energy, that energy comes in 3 forms fat (ketones), glucose, and alcohol and is metabolized into energy (adp), but that energy production (metabolism) is more a measurement of health than a measurement of the total number of calories in. That is what you are ignoring.
Edit: I’m sure you have lost your weight through eating less. But have you changed and improved the actual foods you consume also? Have you begun to burn more through improved dietary metabolism and/or increased exercise? I have a hard time believing one day you were eating nutritionally deficient and caloric dense foods and lost 150 by making no other changes than simply eating less of the same calorically dense and nutritionally deficient food. Even more unlikely would be you being obese eating low calories nutritionally dense foods, and lost 150lbs reducing the calories.