It's almost the same as saying that the off-ramp for a cat to get off a tree is to apply a=g until h=0. It's technically correct, but I don't think it would help the cat to be aware of this.
To a certain point yes, but also no. Depends on which fat you're talking about and which calories you are talking about (calories from carbs without fibers cost nothing to absorb, calories from fat cost more than half the energy they give you) (also if you have a good gut health, some calories are just never absorbed).
Calorie restriction works up to a certain point, and weirdly the benefits aren't linear, and almost flat for visceral fat(i.e: if you're using 2.6 kcal a day and eating 2.4 kcal, you will loose roughly the same amount of visceral fat than if you only ate 1.8kcal, and slightly more 'external' fat (that one you shouldn't care much if you're only interested in health)).
Calorie expenditure works linearly though, but it's hard to out-exercise your diet, and exercise while obese can be dangerous (my ankles still have to be reinforced despite me being under 24 BMI)
calories_in < calories_out seems to be a pretty good formula.