Well one thing I know for sure that is benefitial using fictional cars is that....you can manupulate the performance of the car and get leveled competition. If you are fixed to a set of real performance values, the difference between cars will be rather large. (although car balancing is rather bad in LFS so far it's an ideal that is possible to work on.)
About the point of racing simulations should simulate real world as far as we can, I am not so sure. I am now exploring the world of flight simulations, and it's a rather inspring experience because every serious aircraft they made are accurate not only physically, but also historically, they even find perioded pilots who has experience in that particular plane to review the physics, and it seems the portion of real pilots playing flight sim is quite some higher than the portion of race driver playing racing sims. The meaning of immersion in flight sims, that every switch, every bolts and nuts has to be exactly correct is quite attractive. starting an aircraft from cold is a occasion, so is the actual flying experience.
It's rather different in racing sims however, I own a copy of GT legends because or the amazing lineup of cars, in terms of graphic and sound it does a notable job in recreating the real vehicles, but still, when out on a track, trying to do a fast lap, all of these doesn't seems too important, whether the ignition switch work, whether labels on the dashboard are correct as it is, racing simulation is much more about the actual driving, it occupies your senses so much that the physical aspect is more more important then the rest, as long as the visuals and audio are not so bad in a way that they carry you away from the experience.
Same goes to the cars, whether it has the exact torque curve as a real car or not isn't that much of an importance, as long as it is realistic according to the law of physics. Even if you make a car in LFS, which suspension hard points and wheel dimension is different from any other car in reality, it wouldn't matter and thus stand out as unrealistic, because the inner working is sound, I might even say this is a real car but a real car that has yet been produced, because on paper it's possible to design and manufacture a car with such stats.
That's my point on why real life reference helps creating a realistic simulation, however depiction of the actual object itself is not. And I think as long as you have a good physics engine, it will be rather easy to inject real life datas and create "real" cars.
Think about it, when F1 designers start a new car, they start with concepts base on engineering principles that they know is sound, they do not start base on the old numbers of previous cars and reverse engineer it, because they already know how that part of physics works. Their new car, is basically designed out of fastasy, experiemented in virtual reality and then built in real life, most of the time the end product will behave very close to what is simulated, up to that point it's all down to engineers and their maths, rather then what the driver feels. The driver feedback in the end is just a final check on the actual outcome conceived from a mental point of view, very important for the result, but a driver cannot design a car because the information pool he draws from is different from the engineers.
That's alright in real life because physics is a constant, but in sim racing, how can a real world racing driver tell whether it's the fault of the physics engine, or the data that goes into engine that creates the problem? The driver can tell whether the car reacts correctly under a turn in - throttle lift scenario, but he cannot possibly know whether it's the setup, the parameters, the physics engine, or even the input controllers, and because they don't spend hours a day messing with a sim in different combos, they cannot cross check and unlike us, knows the flaw in the physics models.
and probably to a simillar amount of corners as a racer does.
