I may be missing something, but isn't the focus on calories about weight gain, not feeling full?
Feeling full matter a lot. It drives when you stop eating, fetch something else to eat and also is related to how active you are. It drives whether your thoughts are turning back to figuring out where to get food or whether they happily go elsewhere with no effort.
Yes, “all calories are the same” is a statement about thermodynamics, not the subjective experience of eating.
People who value other things higher than how it feels to eat and be full, like athletes and actors, can accurately manage their weight with calorie counting. It’s often not a pleasurable experience, but they subject themselves to it to meet their professional goals.