I had not played a Forza game since the 4th iteration, but I really dont think the AI used to be this dumb and aggressive... I'm glad I didn't buy an Xbox One for this game if what the opponents on this game behave like is the same for the console.
You cannot engage in a close race with the AI, because if you get close to them they behave erratically, braking more than they used to on turns resulting in crashes, or straight up not braking at all and flying off the turns. Also, when there's a lot of AI cars next to each other and you are making your way through, they never allow for a clean pass through the pack since they swerve all over the place and have a knack for pit maneuvering your car even if you keep a neat line....
The most offensive AI behavior though has to be the obnoxious way 1st place AI drives perfectly while the rest of the pack does everything in their power to keep you behind, resulting in races where first place is always 10 seconds ahead unless you engage in scummy AI tactics of playing bumper cars to jump from the back of the grid to the front before the first half of the lap.
It's an impressive looking game, but it has an awful play style.