So it's bugged in reverse then?
I just tested it on Tokyo Expressway for the 1st lap times. And the dificulty settings matched the times the AI did. It was faster on Hard, middle on Medium, and slower on Easy. But the thing is that the time the AI did on Easy and Normal was pretty much the same. And just faster on Hard.
It might be a case of the AI times changing when you go back to main menu and enter the race again. As it happens in some missions before.
In my tests for the 1st lap time on Tokyo Expressway done by the NSX'17 AI car, these was the results:
Easy - 2:28.774
Normal - 2:28.722
Hard - 2:27.243
R6Rider
From my experience, the race cars perform worst than the street cars tunned in this race. Gr.4 cars are too slow, and Gr.3 cars need to be detuned and become also too slow for the top speed on the straight.
One thing i noticed while watching the AI drive during the replay is that all cars are tunned, they all have aero parts to increase downforce and dunno what under the mechanical tunes. The fastest AI is also using Soft tires, but in my race that made him pit 2 times and losing to the AI that was using medium tires by the end of the race.
In the Straight the AI NSX reached 305km/h, the GT-R'17 AI reached 308 km/h but is using medium tires so its slower on the turns but it came out on top by the end of the race compared to the NSX.
Pretty much my recomendation for this race is to use a powerfull street legal car that can reach 305-310km/h during the straight. And just do some tunes to help with grip and stability during the turns, like suspension and aero parts for downforce.
For my GT-R i also aplied a wide body-kit and a balast with 200kg to decrease the pp so i could use more power for the straight, the extra weight makes the car harder to break, but thers only 2 turns where you need to break hard.
One of my 1st tries in this race was using the Diablo and on straights that car was overtaking everyone, but i could not control it on corners with the wet track and hard tires. Thers probably alot stock cars that dont need much adjustments to win this race, but i had fun finding a good balance for my GT-R tune and winning with a car i really like.