Custom championships won't be in at launch but they are talking about including it soon after. I find the AI very good in AC but I rarely race them, only a handful of times when preparing for an online race. I find them on pace, they challenge for position, they don't rear end you etc. They do make mistakes once in a while too. If you drive against the AI like you are really racing, that is, no divebombing, no rubbing guys out, respecting the damage level of your car etc. I think one can enjoy racing against them and most drivers will find it challenging.