The reason exercise scientists and nutritionists use the calorie as a universal measure and assume that all calories are equal is because: it’s easier to conduct research
Personally I do not diet, I do not advocate for diets. I dislike diets not because they are not effective but because they are almost always not fun. If you don’t enjoy it you’ll have a hard time making it a lifestyle and soon you’ll fall off the band wagon. This is why diets have such a high failure rate.