Ally,
Yes, if the gca can't visualize the details, perhaps they shouldn't be a gca. Or, the are a below average one, at best. I have often joked to the big contractors and some individual shapers, that they shouldn't work so hard to make lesser architects look good. Of course, that is their job. As Brent Wadsworth once told me, they try to make it as good or even better than the plans show.
Another problem is communicating vision. I gather that if the gca is their own shaper, that is a bit less of a problem. Both the artistic shaper and artistic golf course architect are probably visual learners, so sometimes I have had long discussions with shapers about something, and when I ask if they understand, they nod yes. I can always tell by the quality of the nod whether they really do or not. That is why those red line field sketches are so popular among architects, but even those don't always communicate what we feel needs to be changed. Hence, why 3D renderings and sketches can be so valuable.
And the stuff I have learned from shapers (and perhaps, really from other gca's as they have just shaped a Fazio job or something) is stunning. It's little and hard to explain things, but for one, if you build two mounds/earth forms, the swale between them should never be exactly 90 degrees. The best shapers alter that by a few degrees, creating that attractive "wobble" shape.
Similarly, if they gently orient any line of earth forms around a green more to the natural lines, rather than 90 degrees to the edge of the green, things usually just look so much better. In the old days, with more horses, but oddly, less horsepower, shapers had to follow the natural angles a bit more. No. 10 at Prairie Dunes is one great example. And, I have seen lots of Fazio greens where the surrounds follow the terrain as much as being oriented to the green (might be that shaper, and not TF, can't be sure since I wasn't there) but they work great.
Another shaper taught me how skylines of nearby earth forms can cross and disappear behind the other. I fought one shaper once when he had been adamantly taught that skylines should never cross. Don't know why.
Again, easier to point out in the field than explain on a screen.