What I said does not in any way imply or infer that "all cars are the same". Once again, you spun my words in an effort to tear down a very good statement that I made because you don't understand it. I'll try to explain.
You said one thing that is true. It is impossible for all cars to be ideal for all track shapes, conditions, and driving styles. That's why the baseline setup for any given chassis manufacturer does not work for everybody: different track shapes, track conditions, and driving styles.
Any car can be adjusted (from the baseline) to meet the driver's needs but it might not necessarily be comfortable or feel like a meaningful compromise to the driver. What do I mean by meaningful compromise?
There are some very highly respected drivers at the national level that have a particular driving style and the car needs to be a certain way for them to be comfortable and successful.
What a great many people fail to understand is that almost any setup adjustment you make is a compromise. The baseline setups are designed to be a happy medium but it may not feel right to every driver. From there, there are a million ways to tighten or loosen a race car. Some of these changes will make the car feel better to the driver but not make it any faster on lap times because it compromises something else. But some of these changes will make the car feel better to the driver AND make the car faster because it doesn't compromise as much (if anything noticeable at all).
For example, someone is trying to tighten corner entry because the driver says it's too loose on entry. What do you change? I can list about 20 things that will tighten the car on corner entry. But only maybe three of them will make the car better on the stop watch. And for a different chassis brand, those same three adjustments might slow the car down. Different designs, different baselines, different reactions to changes.