GT cars are easy to drive as they have a lot of power and grip, that allowes for a much greater room for error, you can easy power slide in them. WTCC RWD on the other hand are under powered for its weight so to go fast in corners one needs to intentionally break the traction at the moment of entry ( i do it with braking, with the rear sliding and the front pointing the inside of a corner ) and then you are able to power slide. You can still ride curbs in them but one needs to be much much more careful while doing so, steady power ( no rapid deceleration or acceleration ) and off weight as much as you can. It takes A LOT of practice and determination to be fast in them, most people just give up and go for the easy option in FWD. In the propa hands the RWD WTCC car will be unbeatable, even mild/medium contact with other competitor won't spin you out straightaway, one can just make bigger slide and easly recover, it really takes a hard shunt at the wrong moment to completely lose control. The reason most people will lose control with the slightest touch to the rear is becouse they try to drive it without sliding, when the slide happens ( like in a shunt ) they don't have the exprience and practice to control it. With those cars using the throtle and brake to steer is as much important as the steering wheel itself, or even more.
Patience and practice guys and you will enjoy the Real Driver's Car, sooooo much more fun then the FWD's. GL.