From your first Post about it in this Thread, for me, it sounded as if it is a Problem with this Mod only.
But when you now say that it is the same with S397 Cars and other Vehicle Mods too, it more seems to be your personal Opinion about how it should look.

As said, there are many Things that affect the Look of the Cars Paintwork.
Started with the used Texture, over the Material Settings, the Daytime/Sun Angle on Track, Track related Settings and not to forget the ongoing Work at the Games Code.
And i think it is just like it is in most of such Cases: you can not please everybody always.