The slow AI in Gran Turismo Sport has a few reasons to exist, here is what I can guess from my 20 years of playing racing games and my 6 months working in an actual PS4 racing game:
· The AI drivers obey the laws of physics within the game, probably working with the same inputs too, that is a good thing if done right. The issue is that Polyphony might have failed to make them have the reflexes players have so they play it "too safe" and cannot be as fast as B-rated players (I am B-rated and I am, on average, around 2% faster than the HARD drivers in custom races).
· Remember the "inputs" thing? Well, in a way, AI drivers have less things available than we do. They cannot tune the car and, as far as I know, they cannot use different fuel maps. They do have some sort of strategy even if it is poorly calculated, they know when the fuel window opens. If you want to have a "fair battle" with them on longer races, always go for a full tank of fuel and always use the richest fuel map.
· The game only has ONE RACING LINE PER TRACK. If you use a slow car around a fast track you are going to see the AI drivers take unnecessarily wide lines around corners that are 100% flat. Cars with unbalanced behavior suffer from this specially because they take lines that are incredibly inefficient for them.
How to solve some problems for future Gran Turismo games?
· I suggest Polyphony goes for what a little game called SODA Offroad Racing did in the mid 90s. In that game you could build your own tracks and the game would then spend some minutes trying to figure out the best racing line possible by running dozens of simulations with each of the game's 3 vehicles (a lightweight buggy, a pro-2 pick-up truck and a pro-4 one). Polyphony might not be able to do that with all ¿1000? cars but they could take a few "generic" ones (SuperFormula, Red Bull Standard, Red Bull Junior, LMP1, GT500, GT3, RWD GT4, FWD GT4, AWD GT4, K-car, vintage muscle car, etc) that could serve as the base for all cars to follow. The lines taken by the AI drivers would make a lot more sense, that is for sure.
· There should be events for "bonestock" cars and events for tuned cars, BoP is not enough. In the 2nd type of events, cars with very obvious problems in the tuning side of things (the gear ratio of a lot of old cars and modern sports cars) could be somewhat optimized to better suit the racetrack.