I don't think the science is ambiguous as to why carbs can be problematic.

The problem with carbs isn't that they are necessarily bad, but that the bulk of easily available food is mostly non-fibrous processed carbs, which leads to overeating, reduced nutrient density and less appetite satiety which makes overeating very easy.

Walk to any grocery store and most of any boxed food provide energy as carbs. At 2000 calories a day, that's a ~500g (4cal/g) budget for protein & carbs. 4x nutter butter packages burns through 1k+ calories, which I've seen family member teenagers do while junk fooding it up, then eating multiple 1k+ calorie meals. There's a ridiculous amount of inadvertent overeating that is occurring with the types of convenience foods available today.

Most naturally occurring carbs (rice, fruit, wheat, quinoa) are generally loaded up with fiber which satiate appetite, reduce insulin/sugar spikes, etc. Most people don't eat raw or minimally processed carbs through. It's generally consumed as soda, bread, chips/snacks, etc, + whichever meal is being consumed that day.

The body's metabolic process is pretty straightforward. Sugar is stored as glycogen in muscles & liver. Fat/Lipids are stored as fat in the presence of insulin. Protein is used for tissue regeneration and also converted into sugar through gluconeogenesis. Caloric excess means extraneous fat is stored, with an additional burden placed on the heart to support the additional blood flow to having more "body" (more capillaries), while caloric deficit leads to the consumption of the fat reserves.

People would be healthier in general by merely consuming higher nutrient density foods and staying at a proper caloric maintenance. Weighing food out for a week usually opens people eyes to the portions they are consuming. A serving of cereal seems okay at 120 calories, but in reality, a "bowl" is like 3-4 servings when actually measured out.