One of the numerous facts that you are assuming but is not true: all the calories that enter the mouth enters the blood stream. Actually, absorption from the intestines to the blood stream is not constant from one person to another.
I’m not assuming that at all.
If you want to claim that you can eat 2400 calories, burn 2000 calories, excrete 400 calories, and not gain weight, why do you think I would disagree?