The trick must surely lie in the preparation. We aren't Neanderthals and cook our food, and I'm sure we can find a way to make maggots or other insect larvae appetizing. As you mentioned, they are highly nutritious.
Harmless by themselves, perhaps, but if they make some ultraprocessed foods more appealing are they entirely harmless? I think it's fine to make beet juice in the kitchen for our own uses.
Counting calories is inherently inaccurate, since the margin of error for measurement on food labels is 20%. Calories are a unit of heat energy and aren't all that useful for the management of ones diet.
fail to meet our goal and rebound to the same weight - if not heavier
If calorie counting isn't working, and there is a rebound, then perhaps there is something else in our bodies that underlie the condition of being overweight that isn't just how much you eat, which I think you described well in the paragraph after.
rural village scenario
Unfortunately most of us are unable to go live in one of these, but in that scenario you described I do agree that the obese person would get a lot healthier. The removal of all processed foods would have done a lot of good by itself. Better sleep, good circadian rhythms, etc, would all contribute considerably too.
I didn't know how to keep it clean before, and it used to bleed and such so I went to see the dentist. I'd recommend you do the same thing - if you get a strange taste in your mouth or anything at all causes you concern it's best to go see the dentist to make sure it's okay.
In my experience food particles getting stuck in there is the main cause of any problems I've had with it. I fastidiously keep it clean now and it hasn't bothered me since.
Cooking for those you love