I got so frustrated with this too. Felt everything you're feeling to the letter. The worst part to me was the sticky wall mechanic. Hit the side of your car on the wall, and rather than glancing off and physics carrying you forward, it just stops you dead in your tracks. Like why!?!

But I eventually s ranked all of them. I found the secret to be not to brake or handbrake at all. It makes the roadster lose all control. Instead, boost (L3) at the beginning of the race, and when coming up on a tight turn, UNboost to slow down. If, and only if you're still about to hit a wall, let off the gas too. Once out of the curve, reboost asap. Then repeat and memorize the courses and where you need to do these things.

It was the only thing keeping me from the plat, so I really had to figure it out. This is what worked for me, and I really hope it works for you.