I'm not affiliated with GS and am not trying to defend what they told you...that said, there's two sides to every story.
Roadside service providers, GS, CoachNet AAA etc, put out their service contracts to bid and contract with certain providers. Part of that contract bid process means their reps will have the proper insurance, bonding and necessary knowledge to provide a certain level of service when they respond. By calling another "provider" on your own, you cannot be assured they have the same quality provided by the service contract. Their rigs and equipment must meet certain standards. I've seen tons of used tire shops that offer to "fix flats" but I wouldn't want them anywhere near my coach. McDonald's is successful because of the food quality and service you, and they, expect from each and every establishment. In other words, you know what to expect by visiting their facility.
While you may have received adequate service from the $86 guy who came out this time, next time you might not be so lucky....
If you feel GS does not provide you the "value" you perceive you should be getting, you should probably drop the coverage and use independent providers in the future. Before I'd do that though, I would send a personal email to Marcus and see if what you experienced is now the norm or an anomaly.......Dennis