Realistic and Real are two different things to compare when comparing racing simulators, and under my understanding, LFS is not realistic, but feels real.
I explain: realistic IMO means that it will simulate real things, like real cars and tracks, and will behave like real cars. LFS does not simulate real things and dont behave like real cars, at least it doesnt feel real.
In the other hand, LFS feels real, within its own world and laws. Once you are there, you are in, and you feel what is happening.
For a long time this real feeling was a privilege of LFS players, there was no other simulator to give the same feeling. After NKP and iRacing this true changed.
Today I can see only some good things that still give some advantages to LFS, and that is just price, easy to install, and user interface, because the physics is not better than NKP or iRacing, and in fact it is not at same level, and fictional cars and tracks cant compete with ultra detailed models from iRacing.
About rFactor, the subject of this thread, I think it advantages is only the great netcode and the price, because it has not a good feeling, the physics are not that good, and the "mods" thing is a mess like no other.
I gave up LFS for a long time, but I still keep some hope and wait for the day we will test Scirocco in Hampshire .