Right but it’s not a maximizing theoretical loss function, it’s picking a specific expenditure of energy as the goal - kinetic energy of the bit. Particularly

Right but it’s not a maximizing theoretical loss function, it’s picking a specific expenditure of energy as the goal - kinetic energy of the bit. Particularly you don’t know the goal of the bits motion, and the work the energy does could translate into the machined parts final configuration or something else. The goal isn’t specially to account for energy in some full final system but to give an optimization function for the tool itself to maximize. You’re looking at it from a physics point of view rather than an engineering point of view, the engineering view is practical - how much energy is expended to get a certain amount of work done by the bit and not doing other stuff like heating the environment, making noises, inducing vibration. The metric is a practical one, and it’s never meant to capture the entire energy transfer dynamic in a physics sense.