What I never liked in particular about PC sims is that no matter what you get screen tearing, I mean even at constant 60fps you look on the side around and understand this is no Gran Turismo smoothness, there is some kind of delay, hiccups like all the time, that brakes the realism a bit. The graphics in absolutely all PC sims I played look cartoony, to me at least. I really believe because I see it and feel it that GT is above all sims I played(never iRacing though), physics wise in the first place.
Also GT is plug and play, while with a PC things are a bit scary when you think about different kinds of incompatibility, even a software in the background can affect the game performance. I hate PC for all kinds of problems that it might bring along the way.