I also don't like the idea of forced default setups. I never use default setups. Some might say it levels the playing field due to everyone running the same setup, but what if the default doesn't suit my driving style, but suits someone else's?
Me and a friend had this conversation about Race of Champions. I said it's interesting seeing how drivers from different disciplines go against each other in identical cars. He said that the set ups are fixed for each car, so the drivers can't adjust them to their liking, which in theory could work for one driver and against another driver, making any comparisons in RoC pointless. As an example he pointed out one successful rally driver who went poorly in the rally car, due to it being set up way too stiff for his style. It's a bloody good point. Having one make races will level the playing field. Forcing everyone to run one set up will not, because one set up will always suit some people better than others. Being able to set the car up yourself will show not only your driving skills, but also your set up skill.
So I'm with you mate, it aint my cup of tea either.
This was probably already addressed but I CBA to read the whole thread at the moment. But, you actually described exactly why fixed setups are a true test of driver skill. A truly skilled and well-rounded driver can jump into any car with any setup and be quick with just a bit of practice. Adapting your driving style to a particular car is much more of a challenge than adapting a car's settings to your driving style. So in the scenario you describe with the ROC, the best driver is the one who is able to adapt to a variety of different cars quickly and be fast in all of them, which is exactly the point of the ROC. It's not about seeing how is fastest with their preferred setup, it's about who's able to adapt the quickest to any random car with any random setup. A driver who can be the fastest in all three of the ROC cars deserves to be the champion, but a driver who can only be fast in those cars when it has a preferred setup does not deserve to be the champion.
When I hosted GT5/6 clubs/races I always used the "no tuning" option, for a variety of reasons. For one, it made it easier for someone to just grab the car and jump in at the last minute without having to worry about other people being way faster because they had spent a dozen hours testing and tuning the car. I wanted it to be about who was the best driver, not who had the most time during the week to perfect their tune. Another reason was that it made us more versatile drivers. After racing several cars with their default setups I learned to be able to feel the nuances of each car and adapt to them, and before long I could jump in any car and adapt to it within a few laps and be quick. I firmly believe that time spent behind the wheel makes you a better and more well-rounded driver than spending time in the tuning garage. You can often make a greater improvement on your lap time by adjusting your driving technique or your corner entry than you can by adjusting a suspension setting. And you can apply that technique to a just about any car on just about any track, without ever touching a spanner.
But we all have our own likes and desires, forced default setups happen to be my preference but that doesn't mean it has to be everyone's preference. As long as they allow us the option to enforce a default setup or allow full tuning, then everyone is happy.