I'm not sure why people are raging at the MX5 so much. It's fairly drivable inside a tight court, which means you shouldn't expect LFS slip angles with a car that has half the steering lock of any LFS cars out there. Don't expect to correct slides with your limp cock, you actually have to improve your reaction time to catch those nasty slides, but driving in a way that those won't happen ensures you are fast too, and not only keeping it on the grey stuff. I think MX5 is a great car, even for rookies. It teaches them how to keep a car on the road, how to not overdrive cars (none of those iR cars tolerate it anyway) and it brings great racecraft on top splits. You can literally touch other cars, cause there is no velocity, therefore you only get 0x after slight touches.
About the ratings, I agree with Deko, it doesn't take more than a few days to get A class, and feels easy to maintain a good ammount of it. If you are seemingly losing SR, then just go back to MX5, drive a few clean races, which are quite simple, and gain SR. It also feels like free iRating after the RUF Cup main SOF races.
If you have difficulties reaching a certain Safety Rating, that probably means you belong there. Reacting to what happens around you is part of the racing, not going off the track aswell. C 4.0 to get GT3 is a piece of cake. Participating in GT3 wreckage is not, and I didn't even see non-top splits yet but they still turn into wreck fests. I rather stay in the CSpec, which is less mainstream, but at least all the drivers are enthusiastic and good at racecraft and almost on-pace. I also enjoy the car a lot more than GT3.