I like this game but the AI behavior is too arcade. Cars are too fast in circumstances where they should be less. For example if I am next to a car and the AI has wheels (two or four) in the sand or in the grass they should be slower than me on the asphalt .. instead these whiz like missiles it seems that they have a hundred hp more than myself. Sometimes, even when exiting the corners, if I accelerate first and they have braked, they overtake you on the straight at absurd speeds (this does not happen with other games). Second: there is no windbreak (?) or get in the wake(?) (I don't know in english).... You can follow a car for ten seconds at the same speed and cannot overtake it. I do this quietly in games like ACC and RF2. Please try to improve the AI because this game deserves it.
Grass actually doesn't really slow you down in a straight line in real life either. You mean drafting. That's obviously in the game, but the strength of the effect depends on the car. In some cars, the effect isn't very strong, just like in real life.
How can a car at your side accelerate and move 10 meters ahead of you? Or when on the straight you are at full speed in sixth gear and the car behind comes as if it were in seventh gear! With the WTCC I can follow a car on a straight line for twenty seconds without taking a meter. I've been playing driving games since 2002 ... I know what I'm talking about. So please humanize the AI.
I only had such a behaviour with f4 and Alex wrote, that it might be a setup "issue" with AI at low downforce tracks. Yesterday I drove Shanghai with FR3 and on the long straight the AI behaved normal depending on how good their or my corner exit speed was.
I generally find that the AI issues are of a pretty subtle nature. For example, with touring cars they generally really like fast, flowy tracks as opposed to slower tracks and tight corners (i.e. you have to lower your AI setting for the former). The behavior of them sometimes having "super traction" in the grass/gravel is a little bit of a bargain with the player--if you crowd them off the track they'll get the extra traction as opposed to wreck you. Either way you don't "win" by being a dirty driver; the way R3E does it just lets you continue your race when you make a mistake as opposed to ending it. R3E makes a lot of those decisions and it's one of the things I personally like about the sim.