I too was in the same boat as you. But give it some time and the AI will actually become a lot of fun to race against. Below I will give my reasoning and some tips for this experience.
My first tip is practice, practice, practice. If you are coming from the GT series, you will have a hard time adjusting to FORZA"S drivatar AI system. Simply because IMO the GT series AI did nothing but follow a near perfect race line every race. To me that got very boring. The only challenge in the GT races, were when to time your pass exiting a corner. The drivatars on the other hand are tough to get a good run on to pass them when exiting a corner. Not to mention the drivatars will actually block you from advancing thru the field. Once you learn their tendencies, like the brake checking and the packs they move in. The fact that they aren’t brain dead AI like every other racing game is very refreshing.
My second point, (not a tip just a footnote). I’d said it would be safe to assume that you have the AI Limit aggression turned to ON. If not make sure you do that also. It doesn’t seem to help as much as you would think it would, but it does help the unpredictability of some of their more aggressive moves.
The particular track you mention, Bathurst Mount Panorama. I also find it frustrating to get a clean start there. But this is my third tip/point. Although some may disagree with this. When starting a race, say mid pack P12 or P11, hold you brake trigger lightly and also hold your gas trigger about where it needs to be to launch the car without a lot of wheel smoke. The very second the race starts continue to hold the brake until the outside car starts to go by you and then release the brake launching the car down the straight. If timed correctly this will imped the cars behind you for a brief moment giving you some breathing room ahead of you to 1) not get hit from behind and 2) not risk hitting a car in front of you because there is no place to go. Another thing to exploit at Bathurst Mount Panorama, is lane choice. You want the inside lane closet to the pit wall if possible. Either by default or from a Plus 1 or Minus 1 Grid position MOD card. Every track is different and each track has a good side and a bad side to start from. I realized after awhile that the AI basically only responds to your pace, when you brake and when you are on the gas. That is why the brake being held at the start of some tricky 1st turn tracks may be helpful.
Most tracks you will have no problem getting a clean start within a few attempts. But Bathurst is really a tough one sometimes. I know this works because I run the R class Modern GT cars and the NASCARs at Bathurst regularly in free play. The NASCARs in particular are very tough to launch and not hit or be hit from behind on a standing start at this track. But I have done it many times both with and without the brake holding method. That is with no upgrades to the cars SPEC class only. Just some minor fine tuning if the car comes with tunable parts.
You can also mitigate the AI’s craziness by driving in the middle of some of the narrow tracks like Bathurst and parts of the infield of the 24HR Daytona track. The AI seem to back off some if you are keeping pace or just a slight bit faster coming into a narrow part of the track. But they will also come flying past you if you are off pace or braking at the wrong times on long straights. Basically what I am saying is after a few runs on a track you really like you will know where it is safe to brake and which side of the track you want to be on approaching a corner to not get rammed from behind.
My next point I bring up kind of ties into the previous thing somewhat. I can’t confirm this but I have read about it on these forums in a couple posts. I can’t remember the exact ones. But just recently I experienced it myself. I don’t know what your driver level currently is. But somewhere between driver level 190-200 my AI drivatars became much more behaved and very good racers. From driver level 0-190
I could pass mostly all the drivatars on the outside with ease going into wider corners. They would always surrender that line and never attempt to block it. Now after the 190 or so level it was like a light switch was turned on. Now I must pass almost always on the inside and even then the drivatars put up a fight. No more breezing by them on the outside line. I don’t know if it’s true but I think as your driver level increases so do the drivatars ability to mimic your race choices. The lines you take and the way you like to pass seems to evolve with the driver level. What I get out of this is that the drivatars don’t necessarily mimic the names attached to them. But instead your own driver data is collected and used to train the drivatars that you race against to give you the best match they can.
So overtime it is like racing yourself but with a twist. That’s just my opinion. But from what I have observed the more I play the better the drivatars get and seem to be able to adjust to my driving style.
Like I said before I was in the same boat you are in. New to Forza and baffled by the AI. Just give it some time and patience. By the way I don’t count a race complete or won in career or free play unless I finish ( 1st -free play or 3rd or better career ) with ZERO contact. When I say ZERO contact I mean ZERO. I will maybe allow myself 1 very small graze of car if I am deep in a race set on PRO AI or higher. But only if it doesn’t affect the outcome of the race. I self police myself. If I hit a car I restart until I get it right. I also don’t use rewind. Which by the way I am sure you probably already know the AI difficulty setting really only pertains to the pace of the field of cars, not their said driving skills. So for me the challenge is not how high I can turn up the difficulty but how many positions I can improve my starting positon without making any contact with other cars or exploiting track limits.
Which brings me to another point about Bathurst. The first turn at the start of the race would be one exception to the no exploiting track limits rule. Ironically it doesn’t help your grid position so I don’t mind doing it. If you have the inside lane to the pit wall. Keep your pace and cut to the edge of the grass immediately and fall back into the grid of cars. You may lose some track position maybe a lot of track positon depending. But for me its an alternative to the brake holding method I mentioned earlier. The only time in a race I would exploit track limits are to avoid an accident. With the brake holding method, the timing is everything. It may take you a few attempts to get it right but when you master it. It really makes the standing start of difficult first turn tracks a lot of fun. Besides that you really never get an advantage from it. All the back markers are still behind you and the cars ahead of you are there waiting to be passed cleanly and not demo derby style.
Lastly I think each time you start Forza (launch) game from main menu. That it supposedly downloads new information for the drivatars. I have no clue how true or false this is. But I have observed
some differences in the drivatar behavior during different times of game play.
Well I hope some of this helps. But the bottom line is just stick with it. If you love the game as much as I do the bad experience you are having with the drivatars will take care of itself overtime. You will learn their tricks and also learn some tricks to survive free play/career races damage free with ZERO CONTACT.