Maybe Ross was just a tad strong in his statement to what he really meant.
Most architects will tell you that they don't like flat sites, but the trade off is they can implement their design philosophy more perfectly. That is, if they have a preference for a certain yardage, par, par rotation, etc.
I also prefer selling to a client who has a flat site, as I think it gives me an advantage. It seems like no other architect has designed more courses on flat sites than I have, which should give me an edge on the experience ranking.