I don't know if the AI gets free traits off of the difficulty settings but ALL the AI units in my expert games have bloodthirsty/strenght/ironskin. And these can be stacked depending of their units' traits as well.
Made the mistake of creating charge/ironskin/strong infantry units and now i'm facing them every game with an additional 3 traits (given 2 of their traits are redundant/stacking). Pretty hard to fend off plenty of Blunt&leather infantry running five tiles on 1st round of combat with minimum of 20 defense before turn 80