On the AI topic, I think there are a few smaller issues (well, not quite small) that compound together to make a bigger issue.
I've noticed that at least in some cases (maybe all?), the AI cars have different performance parameters to the player car. I've picked up on some fairly obvious examples of them being much slower than the player in a straight line, but having far greater braking and turn-in capabilities (and before you ask, yes, default setup, no changes).
The other issue I see is the way they "see" what's happening in front. I think their "overtake" state happens far too quickly and that corners and different parts of the track mean absolutely nothing to them. You see this in effect when one AI car passes another on a straight. After getting a good run out of a corner a bit of a slipstream, instead of gently adjusting their line, they wait until the last moment and make a very sharp and aggressive change of direction to go around the other car, rather than past it. In cases where there is a big speed differential (a multi-class race, for example), the sudden nature of this turn can be so violent that it causes the overtaking AI to need to brake to regain control. Either that, or the high closing speed means that the "avoid collision" state triggers before the "overtake" state and they aren't going off the racing line to pass, they're doing it to avoid a crash.
This all comes together to create an even bigger problem when you have a scenario that is the player braking for a tight corner with the AI immediately behind. Because the player is likely to be braking slightly earlier than the AI, this might trigger the "overtake" state or "avoid collision" state, which causes the AI to aggressively move off line, regardless of what part of the corner or track they're in. I believe this is where the hyper-aggressive corner cutting comes from. Sometimes they pull off line and nail the throttle, attempting to overtake, in other cases they make a sudden avoidance move and jam on the brakes, occasionally spinning out in the process.
These occurances are all the result of settings, reactions or scenarios that have been programmed into their behaviours and definitely are not isolated. You can run multiple laps of the same track and watch different cars make exactly the same moves / mistakes and exactly the same part of track. I've found Monza to be a way to look at the many different flaws they exhibit, as they consistently make some pretty dramatic mistakes that cause problems both for themselves and the player. Curva Grande (the long right hander after the first chicane), the Della Roggia chicane (the second chicane), the first Lesmo and the Parabolica are all corners that are guaranteed to see problems anytime there is an AI car following another car (player or AI). That's four corner complexes out of seven.
The AI in Project CARS do have some serious problems and putting our heads in the sand is the worst way to react to this situation. I'm disappointed in the game, but I won't crucify it - I still get enjoyment from it and see massive potential waiting to be tapped into. But if we don't tell them that this is an area deserving of major development and time investment, what's to stop them prioritizing working on a more accurate modelling of the effects of higher or lower air density on downforce (for example) over something that is far more elementary? You need to master crawling before moving onto downhill mountain bike riding, a concept that I feel the developers may have missed...
