Technically, you can do a lot of car "tuning" on the PC version if you don't mind being a bad boy. Otherwise you guys are correct, you're only going to be able to adjust things that the real life version allows you to adjust.
In real life, the limit is yourself, not the car. You can install tuned ECU even on cars like Ferraris or Lambos, you can fit supercharger/turbocharger, you can fit any tire you want when on track day ( from street to slick with different sizes and compound ), you can change swaybar sizes/adjust them ( some cars allow adjustment from factory ), you can change the springs+damper ( alter ride height, on some supercars with lift kit or adjustable height system - Aventador allows this ), damper adjustment also possible from factory on some sports car, you can add chassis brace, roll cage, you can change the LSD, you can change final drive, you can put better air filter ( intake ), you can change exhaust system, you can change drive mode on cars with multiple ESP profile ( like Aventador SV - Strada, Corsa modes ) or completely disables the ESP.
Does the JDM cars have their speed limiter ? Most JDM cars like R34 GTR, RX7 Spirit R have 180kmh limiter from factory, if wanted authenticity of being restricted to what the real car can do ( fresh from dealership )
Anyway, that just me ranting
I just don't like people saying that a sim has to be rigid in tuning possibility to separate them from the mainstream console games that allow more freedom, for the sake of being 'sim'
When I was back in Sydney, almost all the imports I have driven have mods on them, from electronics gizmo like boost controller, turbo timer to HICAS controller, cold air intake, exhaust, intercooler, turbos, suspension, strut bars, chassis brace, wheels, semi slick tires, to BOV with distinct sounds. Very rarely they stay stock
, even Toyota Crown have coilovers.