generally speaking most people who suffer from diet related diseases are eating refined carbs with fat. The fat could be from animal based products or oil. The refined carbs produce an exaggerated increase in blood glucose which tells the body to store more fat from the meal. this will make you hungry again faster. The combination of refined carbs and fat allow people to eat a lot more calories than they otherwise would.
however eating slow digesting carbs like beans with a slow digesting fat like an avocado is unlikely to cause the same response.
also you are correct in that the foods which make people fat are generally a mix of refined carbs and fat such as pizza, cookies, potato chips, chocolates, doughnuts, pastries, cake, burgers, fries or soda with a high fat meal such as four chicken. people often call a lot of the above foods carbs even though they are a mix.
People who are insulin sensitive can generally exist on a wide range of fat/carb ratios as long as their diet allows them to stay insulin sensitive.
People who are insulin resistant can have issues on moderate fat diets because the insulin resistance means they cannot metabolize fat well. They do a *little* better on low fat diets, though people who are diabetic stay diabetic on those diets.
People who are insulin resistant do best on low-carb diets (or very-low-calorie diets)
The biggest consideration here is probably not what macros are being eaten, their exact ratios, and timing of when they’re eaten relative to each other, but rather what kinds of fats and carbs are being combined.
For example, a few eggs (fat, some protein) and an orange (carb) eaten together will produce a very different metabolic response than eating a melted industrial Kraft cheese (fat) on a piece of mass manufactured toast (carbs, also full of seed oils in many cases). Both combine carbs and fat in relatively similar ratios, yet the latter combination is almost certain to lead to more weight gain, mitochondrial dysfunction, and metabolic issues.
That being said, it seems a diet that’s high/moderate in fat, moderate in protein, and moderate/low in carbohydrates is the most appropriate diet for the average human living in temperate climate zones. If closer to the equator, probably more carbs and less fat. If further from the equator, probably less carbs and more fat.