In F1 2010, the AI was a lot easier and also a lot varied on certain tracks. The AI were made too easy or too hard on certain tracks. In F1 2010, Bahrain and Canada were too easy + many other tracks. Also, Spain and Britian were too hard.
On F1 2011, the Legend AI is a much tougher task and there isn't a major change in diffuculuty between tracks.
As I use a D-Pad, I have to use many assists. I do 100% races with Legend AI and they are a real challenge.
I know what the problem is though. The AI need to change to the way you are driving, for example, if the player uses many assists, the AI should use the assists too, meaning they would brake in the same places and drive in the same way, this would make overtaking more diffucult and make the race pace slightly more realistic. The same could be done with any assist function's meaning you get a hard and realistic race no matter what your driving skill is.