On VH both campaign & battle AI get bonuses (or player penalties) and since CA hasn't commented on them I am guessing they are trying to conceal it so that players like to believe they are on equal playing field when in actual fact it is not.

Battle map: Player gets a 1-2 second penalty delay with cavalry. I can see the AI doesn't get it b/c the moment I use my mouse to issue new orders their units instantaneously change direction whereas mine are temporarily in limbo with the compulsory 2 sec delay.

Campaign map: AI gets insta-generals (captains magically turning to generals), 3x recruitment bonus (agents & maybe units), no crusade desertions, huge cash bonuses and maybe public order bonuses as well. I'm sure there are others. The player penalties include Dogs of War diplomacy, Reputation penalties, Score rank penalties, illogical AI (band together) alliances and a few more that I can't remember ATM.

Even though, VH/VH is the only way to go