Yes and no.
The developers have to deal with licenses and have to use data provided by the manufacturer. For a manufacturer, having a car represented in the game is advertisement, so in the case of simulators, I can see a possibility that they give pretty accurate data, but tweak a little bit here and there to represent their car in a more positive light. Another possibility is what happened with the SF70H, when they couldn't provide exact data due to the car racing IRL, so they gave intervals and the developers had to decide what numbers to use within those intervals. So from a logical point of view, I can not see a reason why a car would handle worse than in real life. Nobody would win from that. Unless it happens with all cars, in which case something is simulated wrongly (tires, general grip, etc.), or the baseline setup is just bad.
In the case of mods, there are a couple of modders who have experience with the car they are developing IRL, can measure stuff IRL, and overall can give a more detailed, and personal interpretation of the car. The number of such mods can be probably counted on one hand and the development takes a very long time, as they don't have deadlines as the developers do. In the case of comparing a car from Kunos and the same car from a modder, I generally trust Kunos more. I have driven a few mod cars that handled extremely well, to a point that it seemed very unrealistic (e.g. DeLorean having as much grip in the corners as the Tatuus FA. It might feel good and drive well but it's pure nonsense).
In the case of the car you gave as an example, it came out before Kunos released theirs. I didn't use it, only tried it, because the graphics weren't good enough for me. Unfortunately, even for myself often, I have very high graphical standards for mods, and I can't do anything about it. BUT even if the car would look nice, I would use the one from Kunos, as that car is balanced with other GT3s in the game. If you have a problem with the Kunos R8 LMS 2016, and no other GT3s, I suggest you look at the settings. IIRC that car has a quite understeery and counter-intuitive base setup, especially mid-corner and exit. If you feel the brakes want to kill you reduce the ABS number, it's pretty high default. Furthermore, I would check out the car in other games, e.g. R3E (free test drive)(or iRacing, but it's very expensive just for that).
However, everybody should sim race for fun. If you enjoy that car, nobody's opinion should stop you from enjoying it