I decided to set up a long challenge today, twenty-five laps at Takahagi Hills in hot-hatches. Trouble is, it looks like this confirmes that the new update has made the AI less competitive, which is a shame. I was three seconds ahead in a Mini by the end of lap one and over a minute by the race's completion (I was being less than optimal due to tackling face-offs.)
That is a shame, as I enjoyed having them battle me throughout an entire race - I didn't see any of them again after the first lap. I think if I had concentrated and not been tempted by the face-offs, I might well have lapped them.
I have obviously not done any scientific tests, but it feels like the AI is a lot slower on Legend.