I would reccommend driving the same car for a while, but change combos, just get used to one car so deep, that You feel it's like Your own body when sitting in the car

If You can handle the car, then You can drive whatever lines with it eventually.
After You've mastered the car, pick another car, drive for a while, for months maybe, then after You have mastered the cars on a very long period You can adopt to them quicker laters, cause You have them somewhere deep in Your brains from that long period of how the cars drive and the speed comes back quick. So finally You are fast in all cars and need just a few laps to adopt
I use to drive only FXO at S1 beginning times, lately I'm a bit inactive, today when driving the gti I was going the WR pace , but I dunno, it felt like I could get them so barely, then after I had done more combos on Fe Later , I was driving Black rev then in the end, I started to feel the car so great in the end, at Gold rev chicane it felt so natural to go trough, the car had become so familiar again to me after all those laps, I went back to Gold rev and it felt easyer to improve that WR too , than the lap I had before
It's all about the feeling , You have to try and go over the edge etc, You have to find out how the car drives in all kinds of different situations
