> We don't "rehearse" a specific drawing, we solve a novel problem in real-time. There's no cached motor sequence to execute.
When you have been drawing long enough there are a lot of cached motor sequences to execute and modify. A lot of art training is simply filling this cache: spend a few hours every week drawing the human body from different angles, in a year or three you'll be able to make it up from pretty much any angle. Add in another twenty years of doing that and experimenting ways to make your tools do more of the work for you and you can dash off "sketches" that a beginner would consider finished paintings that took days to do.