As long as you were near the front of the pack that was true. It's when in heavy traffic that the poor AI really showed itself slamming on the brakes for no apparent reason.
My biggest issues were with the lack of damage to AI cars which all but forced you to play with no damage at all and the fact that cars involved in a caution got to restart in their pre-caution position.
I also heard about massive pitting issues but I always ran races just long enough to avoid having to pit in NASCAR games (15% I think). That forces me to manage my tires to preserve handling until the end of the race without having to worry about AI pitting issues or massively slow user pit stops. I like to be able to run a full race weekend in about an hour or so.