Ian,
You stole my example.
Ultimately, when given a dead flat site, the first real objective is to determine how to drain the land, because even the most strategically conceived holes are worthless if they are under water. And in creating that drainage network, we can build-up the mown surfaces and create a little contour to make things even more interesting. Therefore, some dirt needs to be moved so that the water has a place to go, and that is an opportunity to improve upon what nature has offered.
Undulating property is ideal, but it does impose constraints on the designer. Flat sites offer the freedom to lay out holes to the length and width desired. The 10th at Riviera is all about getting the perfect angle into the green, and that requires width. So, when given a flat site and either a limited budget, or expressed desire to limit earthwork, then width is the key to creating compelling golf holes. That is probably true of most excellent golf holes, but even narrow holes over undulating terrain offer more in terms of stance and lie variability.
TK