I've not played either, so could someone who has offer some insight on this? What's being shown in the GT portion seems like basic path finding, which i'd have thought is easy to implement and comes with minimal resource overhead. Is the lack of it in Forza 6 intentional in specific circumstances, or does it in general act this way (and if so, why?).
Forza Series uses Drivatars which is randomly generated AI which all depends on the skill and experience of the actual players driving.
GT Sport uses regular AI like all the other racers.