I know you want to believe but...when I was in medical school 40 years ago I believed as you do now.
I bought lean cuisine (or equivalent brand) and ate one for lunch & one for dinner and had a boiled egg for breakfast.
I jogged in center city philly through the smog & car exhaust. I drank only seltzer & ice tea w/o sugar.
I had so little sugar that when I mistakenly took a sip of tonic water the sugar was shocking. I know now that there is sugar in tonic water but til that point I couldn’t taste it and didn’t know.
After a solid month with rigid adherence to 1000 cal/day I had gained 5 lb. What I know now having lost 60lb once and 100 lb after the 60 returned in 5 years, is that for me carbs are the perfect food, digested efficiently & transferred as a layer of fat. On my month of <1000 calories a day I chose the pasta calorie counter meals.
The problem with keto diets is not that they don’t work it’s that after 3-4 years on one my body rebels and I don’t feel well. I have proved two ways through controlled eating that for me at least a calorie is not a calorie and that we can only accomplish so much with our genetics. Most scientists working on obesity are investigating which forms of which enzymes are the most important for how food energy is utilized, stored or wasted. There will be a more nuanced understanding & perhaps even ways to regulate food metabolism.
My own experience is different than yours, but in my case that is because of unusual circumstances. At one time I was a very successful bicycle road racer. I rode over 10,000 miles a year. When you reach a high level of competition... on a long ride you can feel when you are burning stored glycogen in your muscles, carbohydrates coming from your digestive system, and stored fat. On a longer ride after 30 to 40 miles most of your energy is coming from stored fat and whatever you have been able to get into your mouth along the way.
Back when I was very active bananas were the “energy bar” of choice. But it took a lot of them because they do not have very many calories so these were supplemented with cookies, candy and sometimes sweetened drinks. Without this you would experience the “bonk” where you were running almost completely on fat. You cannot metabolize fat at a quick enough rate to keep up a fast pace. In competition this means that you will be “dropped”.
Some people can metabolize fat quicker than others... it depends on both genetics, training and possibly the location of the stores being used.
Sorry italicized my own words.