I honestly thought that the program directors on all GCT tours were independent contractors hired by GCT for the specific tour and free to catch on with any other tour company when not employed by GCT. I know that some of the better ones have been hired as full-time GCT employees to manage programs in a specific part of the world. It is their job to sort out all the tour guides in their region and match them up with the tours GCT has scheduled. If I'm wrong, I apologize to you and to the PDs, if my perception has in any way maligned them.
But the main thrust of this thread is how can the PD tailor the tour to best satisfy the majority of the tourists without unduly alienating any of them. First the "power walkers": we had such a couple on our Amalfi Coast and Tuscany tour. The first time they barged on ahead and did not stick to the prescribed route, the PD attempted to rein them in and told them that was the last time she would do it. She stuck to the warning and there were days when the couple went missing until they turned up at the hotel later. It didn't seem to bother them much and none of the rest of us missed them. On the other hand, in Sicily and Malta we had a man, a solo traveler, who used GCT for transportation and lodging and mostly toured at his own pace and his own direction. But he told the PD each day what he was planning and when he planned to get back together with the group. That seemed to work for everybody. Now if they make everyone else miserable because things are progressing too slowly, that's another story. They need to be disciplined, perhaps as much by the other tourists as by the PD.
I believe the descriptions given in the brochures and web site write ups by GCT are adequate. While the actual pace may be slower than indicated, if you are not able to meet the standards stated, you should not take the trip. To expect anyone to assist you, even your traveling companion, is expecting too much, in my opinion. And I don't think separate groups based on physical cabapilities is a very good idea. I, for example, don't have any trouble keeping up with the crowd on walking tours. My feet hurt terribly at days end, but I'm always ready to hit it again on the morrow. When I am no longer able to answer the bell each morning, I will quit taking that kind of tour. One that was "advertised" as being "slower paced" would not appeal to me at all.