This will drive you mad even more than getting your controller settings sorted.
The AI difficulty fluctuates so bad from one track to another & one class to another it's annoying, add a bit of weather into the mix it gets worse, normal rain they're just slow even at 100 difficulty or above, but once the track starts to dry up they get their super speed & sticky tyres back. PUDDLES grrr
I probably spend more time finding a good AI battle balance than I do setting up everything else.
Regarding controller use AI difficulty settings I actually use anywhere between 90-120 & 100 aggression, but I'm not always looking for the win, just a good battle.
Do a few custom races & try different options, the AI are terrible on the first lap so see if there's a difference between standing or rolling starts.
Or do the survival challenge, put difficulty at 120, aggression at 100, start at the front & see if you can defend till the finish or see how many places you lose.