Have you heard of carapace? Its a tool to create spatial lines for drawing
Drawing from model is about being the kind of character that enjoys spending hours tweaking at tiny details and measuring measuring measuring. Anybody willing to sit 3 hours in front of the model every day can learn it, if he understands that he must measure.
Drawing from imagination like Kim Jung Gi on the other hand is about doing that every day most of the day since you were a little kid, and you probably need an innate ability to boot (and that might be some form of obsessive-compulsive disorder / autism...).
> There's very little that can be taught about drawing.
While drawing from the imagination is largely about using the intuition. The intuition can be trained just like the more analytical side of the brain. I can teach you a few properties of rotation/space, etc, and then give you the right exercises, and then you won't need to use construction to draw.
KJG does have some innate ability, and he was clearly obsessed, but it's not actually the bulk of his method. He has a video about drawing scissors. He can articulate nearly everything he is drawing, specifically the function which guides the design. There are others who can draw like him. Look up Tom Fox.
I created a little game which doesn't explain it, but allows you to practice and get feedback: https://cdsb.itch.io/draw-cube