The moment that you accept that macronutrient composition is very important for health and body composition, you acknowledge that in biological system a calorie is not a calorie. If I want to lose weight, I don't want someone to tell me that CICO so I can just eat whatever as long as I stay under x calories, because as you rightfully pointed out some foods are more energy dense than others, cause fewer cravings, and don't spike your blood sugar. With CICO, I can lose weight but get fatty liver disease, or I can lose weight but lose muscle while increasing visceral fat, since fat weighs less than muscle. These are terrible outcomes. People want to lose weight to be healthier and look better; what's the point of losing the weight if your risk factors for metabolic syndrome go up and you still look fat in the mirror?
For the anecdotal evidence you provided, I think it's not as simple as how you've portrayed it, because your body can be in two energy burning modes, glucose burning or fat burning. If you eat more fat while in glucose burning mode (which is what most people are in), it will just get stored as fat and yes you will gain as much weight as the amount of calories you ate. In so called 'fat burning' mode, your body will increase its metabolism to burn off the excess fat. Likewise, if you're in fat burning mode and you eat more carbs, they'll just get stored as fat. This is also anecdotal evidence (sources: https://intensivedietarymanagement.com/who-needs-to-avoid-fa..., https://intensivedietarymanagement.com/smash-the-fat-calorie...), because unfortunately we don't really have good nutritional studies about this.