The thing is Blowtus, if you are used to sims you are used to the visual and aural feedback, with a little bit of steering feedback. There are no g-forces to contend with either, or costs/risks involved. Therefore you can learn about how to pass and repass people, how to take lines and how to improve your lap times, just like a real racing driver would. Put a sim racer in a race car and the basic skills they already know, but they to get used to ignoring the noise, heat and buffeting.
A real racing driver has the same skills about learning lines and what have you, but has to do it in a cramped and debilitatingly hot environment, being thrown around by g-forces and restrained by tight fitting seats and belts, with a heavy helmet on. They will be more used to feeling the car the conventional way, through the seat of his pants, through his arms and feet, and via perfectly realistic sounds. Put them in a sim, and they are completely lost at sea, having no 'real' feedback to work with, fake sounds, dodgy force feedback because the technology hasn't improved since the 1980's, silly huds on screen, less sense of speed etc etc.
I think it's MUCH easier for a simmer to drive a real car than a racer to drive a sim (to begin with at least). That is why when GTR fanboys claim it must be good because a real racing driver said so means absolutely nothing. They'll be judging it in the same way an 8 year judges the Harry Potter games.