Dan
I'm not so sure that there is only one blend of skills that a GCArchie could have which would make him/her any more capable than another with a different blend. Imagine if all GCArchies, like any other, let's call them, 'creative' people, had only one stregth or one group of strengths. What a boring collection of identical golf courses/buildings/sculptures/paintings/urban spaces....we'd have!
Sure, there are obvious candidates in Landscape/Turf Science/Agronomy, but I'd say the 'scientific' stuff has to be equally balanced with Design Ability/Knowledge of History/Knowledge of Golf.
The 'X' Factor definitely comes into play too. The Love of the Game, the ability to 'see' golf holes, and so on...
FBD.