I haven't noticed anything egregious yet, but they just lack spatial awareness. Normally the top 3 or 4 are proficient at hot lapping while the rest can be hit or miss following the raging line.
Yeah that was prevalent on older releases too. With Expert and above difficulties they had some Stick 'Em on the tires and CVTs. I find that grid placement helps. If you can cut down on the few seconds between you and first at the start of the race it really makes a big difference. I've had races where I technically had all of the fastest laps but still lost because I couldn't make up the grid start difference.
Drivatars are my last favorite feature. I don't use rewind so I am often restarting because they take me out in turns or as you state they have an unholy few cars that defy physics. Even in the one make factory spec races they'll do that stuff.
It does feel good when you win a hard one.