There's more nuance to this.

Yes sugar enters your blood stream almost immediately which isn't a bad thing, but not all of it. A large amount of that sugar gets stored in the liver as glycogen and any of that not used becomes body fat.

But also

Yes when you consume fat, it is converted to be used by the body as energy however the excess of that similar to sugar is also converted into body fat.

Importantly, 1kg of fats and carbs have wildy different energy levels with 1kg of fat representing 7,700 calories and 1kg of carbs being around 4,000 calories. So yes it burns energy to convert fat into energy, but you have a lot more energy to burn for the same amount eaten.

This is why carbs and fats have different recommended daily intake levels. Therefore, most of what causes CVD is actually due to overconsumption rather than a balanced meal that doesn't take you into constant excess of either carbs or fats.