FS realism
I have MS Flightsimulator 2002. It can teach you some of the basics of operating an airplane, but it will not fully mimmick a real plane.
I think it is a lot harder to fly the sim than the airplane. I crash my Falcon 50 simulator pretty much every time I fly it. I have yet to crash the real thing.(Knock on wood).
I doubt a desktop sim could teach you to crash a 757 into a building at 450 Knots.