This "machine learning from humans"-approach was extremely progressive when Turn 10 debuted it and in an ideal case it's the most authentic AI possible, which is probably why Turn 10 sticks with it even though a ton of people and reviewers aren't happy with it, all while the parts they aren't happy with could be much more easily addressed with a classic AI approach.
The biggest mistake in the Drivatar tech (in my opinion) is that your friends-list and the Drivatar reward system affects which drivatars are pulled. If I have a lot of Halo friends who buy Forza when it's 15 bucks and play it for 20 hours casually and drive terribly, then, when their Drivatars are pulled for my race on a higher difficulty, they are sped up to be more in line with the ideal AI driving line making them super generic or really aggressive in their overtaking (though, who gets overtaken by AI, right? ...so nobody cares) or defensive maneuvers. On the other hand, if I have some REALLY fast friends and play on a lower difficulty, their drivatars are slowed down artificially in a way where they slowed down in corners way too (edit: meaning, I bump into them mid corner, which is super frustrating) much or don't reach their maximum speeds even on the longest straights.
There should be an option to ignore the friend list and opt out of the drivatar rewards program, so that only Drivatars suitable to my difficulty, type of car and track are pulled without changing their natural behavior.