Regardless content GTS and PC2 are two really interesting and very different games. Like I play GTS mostly for Lexus and road cars, this where PC2 gives only great selection of true Motorsport machines, historic mostly, by today standards.
In terms of physics, GTS feels the same only if you know what you're doing, where in PC2 every mistake is punishing, including dive bombing and hard breaking, riding on edges, nothing will really help in SMS game. Even SC, TC and ABS has all impact on performance, and in GTS they all are like irrelevant, and general poor race craft could be managed.
Competition in PC2 is strong, both online and offline. Bots are nearly record breakers and talented engineers, if you wish them to be. In online, most people, who tries to drive mad like in GTS fail in few laps, generally ignoring tires and breaks temperatures leads into disaster in PC2. The main advantage GTS has over PC, is much wider player base, like 10x time bigger.