Another important point to make: presumably a culture that can perfect drugs and VR to the extent the Culture has can also perfect GUIs. A human should be just as good at using a VR battle/strategy simulator as a Mind.

Expertise in theoretical physics is mostly about familiarity and comfort with the material. If it's largely a dead art and humans don't have the spare processing capacity to dedicate to it on a personal level, it makes sense that it is largely a habit of Minds rather than humans. A human could simulate exotic physics using VR, but they wouldn't have the cultural background that makes such speculation fun or of interest to other speculators.