In our modern era, how many tour pros really could or would put in the time to become real GCAs, not signatories to a plan? If you are a great tour player today, it seems to me that you are just that, with no time for other studious pursuits. The actual study, as a fellow like Mr. Crenshaw has undertaken, is too time consuming for most, I'd bet.
Maybe a guy like Tiger has a real GCA or even a very good CAD guy come in and tutor him, for his first two projects, in his down time. A great (and wealthy) tour player might hire tudors to significantly speed up their learning curve. But, I'll bet they aren't burning the midnight oil, going laboriously over topos, routings, budget docs, and phazing or staging construction plans.
Finally, I'll generalize that the great modern players become signatories to great architectural efforts most often- consultants in the field for tweaking great plans, and sell the work via name association, rather than exceptional architectural work that they themselves do.
I'd also go so far as to say that most good to great real architects are pretty good am players, just not all that good to compete at any significant am or pro level.
(Unless you are Tom Doak, and get to play in celeb pro-ams with the likes of Catherine Zeta Jones!!!) Now that is greatness!