Well the same main quality makes each setter good at what he/she does. CONSISTENCY in your difficulty of movement throughout your problem/route.
Now we broaden the discussion to the never ending "what makes a climb, great, 5 star, amazing etc). In basic terms, I say its consistency. An extreme example, a 5.14 has only a two move section that makes it 14a. The rest of the climb is 5.10. To many who climb ropes, this would be a horrible route. However, to the boulderer, this could be fantastic.
So good ABS setter can create consistency for his grade. So can a good SCS setter. It still means the setter can gradually increase intensity throughout the climb, but it will be withing the scope of that climb. For example a 5.14a (in most competition venues/gyms) should not start with anything easier than 5.12.
In the end Greg, you are a bit crazy. Some kids dont have the true psyche to want to be pumped and maintain climbing, and some really do. Same with bouldering. I have kids who do bouldering just to stay strong for routes, and others because routes just hold their attention......is this getting into a ADD discussion with todays youth?????