Michael:
It's an interesting point; no one ever brings that up about Ballybunion, and indeed a lot of people including me pick the 11th as one of the greatest holes in the world. And yet, the fairway contouring is totally artificial.
Yes, the decks are built into a steep slope, and if it wasn't for them every drive would just wind up down in a massive divot hole at the foot of the slope. A modern designer would try to disguise the "decks" better with more shaping, and for all I know they have done that in the recent renovation, but the simplicity of the decks has obviously played well through the years.
I saw a course in the Canary Islands three or four years ago that had a couple of fairways with 20+ small terraces, and rock walls at all of the level changes. Better still, they allowed golf carts, but there was a path to the side of those two fairways