5 Brutal must be evil side. Player's enemies is 5 brutal. That means 5 different or same spell power on the AI hands. It's not impossible to win. Your team have to play organize with army, powers, heroes, defensive towers... It takes like an hour. Maybe you can found different variant and you can finish it more early. Good luck & have a fun.
ps: AI spot list is: in middle Mordor, middle to right and middle to left is Isengard, other 2 in front is Goblins. It's more better like that.