In the example of rocks I would have to say the composition, selection, and color of the rocks would be 75% of the art. The question is if you saw the actual 3D still life in front of you would it have the same or any impact on you?

Then again, at some point the lighting, depth of field, film choice, paper, developer, printing technique and the understanding of how a 3D object will be translated and transformed by the technical into a 2D print comes into the equation. So maybe you have to flip the numbers, 75% the technical skill of the phtographer and 25% everything else.

A successful print in the eyes of the viewer is probably closer to a 50/50 proposition. If the values skew one way or the other (brilliant composition, poor technique or the other way around) it would lead to less then satisfactory experience for the viewer.