I hope a calories-in;calories-out person sees this and realizes it’s more complex than that.

That doesn't make it more complex at all. It is exactly the reason to track intake, because internal satiety signals are unreliable.

humans aren’t simply biological machines

controlling hormones and availability of the right food is good to have a much greater impact on weight than counting calories

tenacity can only carry you so far

A calorie is a fairly raw measurement of energy. There isn't any way around that.

You can measure calories that enter the body, estimate what gets converted into work and also measure calories that exit the body that are unused or are simply byproducts of the conversion of energy to work.

The calories-in/calories-out point must always be true. You are making points that fit squarely between in/out. There are different processes that govern what energy is stored and what is consumed, but at the end of the day, energy in must equal energy out. (Or, of you want to think about it in raw mass you can do that as well but you need to account for what gets used, stored and eventually expelled. The conversion of mass into energy for work is also a thing, btw.)

If no energy is consumed, energy must come from somewhere to power the body, even when sitting absolutely still. Even with minor imbalances, the body will eventually start eating itself.

I am purposely excluding severe disorders that do exist that may prevent the body from processing fats at all. (Even in those cases, energy consumed can be accounted for.)

Every calorie may be the same as far as energy is concerned, but not every calorie is equal as far as satiety is concerned. I think its fair to think just saying "calories in vs calories out" is quite a simplification of the challenge, even if it is a key part of the equation to understand.

You are correct. But fat comes from excess calories. You are simply making the fundamental point that perceived satiety is not reliable for all people to gauge healthy intake.

There are a lot of factors that come in between consumption and excretion. But ultimately tracking is the only thing that is 100% reliable.