On the engineering level, only one fact matters: change in energy stored equals energy consumed minus energy expended

Bullshit.

There's a hundred factors being identified that e.g. control how fast energy gets sucked up by fat cells leaving you weak and still hungry, versus how long energy is left available in the bloodstream leaving you feel strong and ready for running. Or e.g. how much nutrient that passes into your mouth is absorbed in the intestinal tract. Or e.g. when exercise creates new lean muscle that burns more calories on its own.

The fact that change in fat equals fat stored minus fat consumed is technically true but useless: I deny its connotations. The idea that the calories you take in through your mouth are the "input" and that the exercise you do to burn them is "output" and that the balance between the two is all that matters is false but appealing bullshit that plays hell with the bodies and feelings of every poor fat person who tries to live that lie. Between input and output there is a giant complicated machine and yes the exact form of the input and the exact form of the output and what you ate as a kid and all sorts of other things affect it.