Your observations and your articulation of them are very good. Thank you for them.
I agree with Graydon, though, that there doesn't need to be a yawning gap between those two styles of drawing. Each can be synthesised into the other to a greater or lesser degree, as is necessary and as the artist sees fit. Moreover, even when one is drawing from a live model in a completely retinal way, as you put it, the result is never as good as when the artist uses his/her knowledge of anatomy and morphology (structure) to augment the purely visual. It's like the old Hale saying goes; "First you draw what you see [retinal image]. Then you draw what you know [anatomy, morphology, structure]. Only then do you know what it is that you see."
Juan
