When AI decides to attack a player, how does it judge the likelihood of success in relation to the player's skill?
Maybe the player's win/loss ratio can be tracked in the campaign like a player reputation/legend system?
When AI decides whether to attack a player, they also consider the players win-loss ratio. The higher the player's win-loss ratio the bigger the AI's army needs to be in order for them to attack.
Also the more the player has won battles with underwhelming numbers, the more the AI will take this into account.