In this argument about rim vs disc brakes pertaining to race performance, and therefore speed, there is repeated reference to the weight difference. Of course, with the UCI weight minimum of 6.8 kg (15 lbs), this really isn't a factor because highest-end bikes with both types of brakes generally would be lighter than this and most teams are actually deliberately adding weight to their bikes to keep them from being below the minimum.
References to "rotating weight" are hogwash.
It surprises me that the argument hasn't turned to aerodynamics, because it has long been argued that disc brakes are less aero than rim brakes. Without a specific bicycle design, it is impossible to prove or disprove this general thesis. However, the limited wind tunnel data that I have seen suggests that this also isn't necessarily a factor. For example,
https://www.slowtwitch.com/Tech/Disc...Drag_6073.html