I haven't seen Gullane or the RC, but I have worked with the European Tour, and the architectural merit of the golf course is not their first concern.
They are concerned more with access and infrastructure. There are a myriad of players and sponsors demands.
Which site is more accessible with good, wide roads for thousands of vehicles and semi tractor trailers? (that's articulated lorries). There will be enormous amounts of materials to set up like tents, television production facilities, grandstands and towers. There will be furniture and caterers as well.
Which site is more convenient to hotels, airports, and rail links? Which has better access to communications, especially cell phone and internet service?
Which site has more available buildings on site to house press, players' lounge, VIP lounge, caddies lounge, and so forth? The more buildings with usable space on site, the less the organizers need to pay for temporary structures.
Which has the electrical grid to power all this stuff?
Which club is more cooperative to close for the maximum amount of time prior to the event to prepare the course to the fullest?
Finally, which course provides the best viewing for spectators?
There's more behind the scenes of a Tour event than mowing grass and raking bunkers, or even #&@*ing with the course design.