I'm not sure I can answer that. But an analogy might be something like this:
NFS Heat: not as deep a game as FH5. Comparing the two heat does very little. But comparatively what it does, it does very well. For what it is, the game is a decent game that plays well with minimal bugs. Has good replay value. Car culture in the modabilities of the cars are sufficient as is the painting aspect. Racing and driving physics are sufficient for the style of game. It does what it is supposed to do well.
FH5: It does a multitude of things. It's a massive game. The modabilities of the cars are lacking. Painting is minimally comparable to NFS Heat. For the size and scope of the game I would expect more.
Car modifications are unchanged from FH2. And referring to engine mods. What is the meaning of the screw driver being representative of the highest level of upgrade in the Ignition upgrade?
But for FH5 it does many things, but doesn't do any of them very well. Actually I should say, it doesn't do them as good as it could.
But it's things like the screw driver, and putting racing suspension on a car lowers the PI. Things such as these and a multitude of other things are the things that tell me the developers of Forza are not real car people.
As for a real car people developer, if we can get Jack Roush or Hennessey or someone like that to make a good car game, then I can answer your question 😉