The AI is a little aggressive since the patch, but aside from the odd incident I haven't had any real trouble with it.
And I've done wheel to wheel racing with the FR2s all the way through Eau Rouge and through Les Combes, so it's certainly doable.
Though granted, looking at the S3 forums the main complaint seems to be in the DTMs which I don't do, so.....
But in my experience, the problem usually stems from not having the AI set to the right level. If you're running with a fixed AI, and it's set a couple of levels too high, the AI will try to get past you by any means necessary.
Try lowering the level a notch or two, and see if that helps any.