I usually wonder the same thing, especially when so many other people are having good experiences with the AI. There's a similar issue in R3E, the AI will often ram you from behind when you go too slow but I use that as a sign that I should be able to take that turn much faster. Once I figure out how to get through that turn faster, suddenly I stop getting rear-ended by the AI drivers. So that's more of a human driver problem than an AI problem, and ends up being a good learning tool. I presume the situation is similar with pCars, if you do something strange that the AI don't expect you to do then you're probably going to get hit (just like you would by a human driver).