Yes I do believe it happens, what I find incredulous is you rate AC AI worse than PCars. The AC AI does have some problems, yes, but no where as many or as bad as PCars.
In AC I have actually had some very enjoyable races against the AI and find them no more or less than what I usually find in an aggressive online room in GT6. The AI in PCars is like GT6 Quick Match, full of dive bombing, grass cutting, first corner heroes.
On that we will have to disagree then, however the issues you are describing in regard to Pcars are not ones I have come across regularly in quite a while, yet braking on the straights, pitt maneuvers and being driving into from behind I have experienced regularly in AC.
Its certainly not helped by the AI cars seeming to not suffer the same consequences from contact as the player does.
Its not as if I'm alone in thinking this either, this si just one of the reviews that points out the same issue:
"The chief offender, however, is the opponent AI, which regularly pays no mind to your presence on each circuit and is particularly deft at muscling you onto the grass and turning your car around by poking its nose into gaps it really should have thought better of. This is where the top-notch driving dynamics Kunos has massaged into all the available vehicles becomes a double-edged sword, because it takes very little to unsettle your car at speed. Even a mild tap on the rear fender can and will spear you right off the asphalt, and there are no consequences for the AI for shunting you off. Frustratingly, opponent cars seem curiously immune to any loss of control when the shoe is on the other foot. Make a little contact via an overzealous overtake and you’ll generally come off second-best, while the AI peels away unaffected. It’s telling, perhaps, that in Assetto Corsa all I want to do is stay away from other racers entirely, though in its Pan-European peer
Project CARSI relish the aggressive, doorhandle-to-doorhandle pack racing.
But it’s not just their racing etiquette that is wanting; it’s also their common sense. I’ve raced several events over the past few days where the entire field has entered the pits on the penultimate lap of a four- or six-lap race. I’m totally befuddled by how such a weird bug could survive a trip to retail and it helps make Assetto Corsa’s already chore-like career mode feel even more untested."
Source:
http://uk.ign.com/articles/2016/08/31/assetto-corsa-ps4xbox-one-review
The ISR review mentioned pretty much the same thing and Kunos have already said they need to look at the AI, as many have also pointed out it appears to be a few patches (at least) behind the PC AI.