The engineers that create formula 1 cars have no idea what its like to drive a formula 1 car, other than from what they know from knowledge, yet they develop the fastest cars in the world, along with the accurate simulators, but they don't drive the cars. Physics are something that can be learned through education just as much as through practical application.
As far as the comparison between iRacing and FVA are concerned, I prefer the FVA, the way the brakes work and the tyres react appears to be more realistic (this is something that is widely discussed on iRacing forums, brakes especially, and is generally accepted). However there are aspects of the iRacing car that I think feel more on the ball, the real thing is likely somewhere inbetween both of those, and different to both at the same time. No simulator is going to be perfect, we all know that.
If you own Rfactor, then you can try out the 2007 BMW Sauber car, which is surprisingly close to the feeling of the iRacing car, they have their differences as you would expect, the feel of the sim alone is different, but those 2 cars are very similar to me, when i jumped into the iRacing car I was able to drive it in exactly the same manner after driving the Rfactor car, however the FVA requires a completely different driving approach, most noticeable on the brakes.