I would like to suggest making the beastmen a settled faction like the greenskins in order to improve their staying power as the AI in the Campaign. Their settlements could be based around herdstones (which are supposed to act as meeting places for beastmen in the lore).
These herdstones could act as outposts for an otherwise mobile faction. This would make the beastmen last longer on the camapign as they would have a base from which to launch their attacks instead of losing everything with their armies (which seems to cause some significant problems for the campaign AI).
In order to show their nomadic nature, the beastmen herdstones could be focused on recruitment, with the hordes themselves acting as the economic centers of the faction, or vice versa, with the recruitment being largely concentrated in the hordes, with the herdstones acting as replenishment and economic centers.
This would ultimately make the Beastmen camapign more dynamic and intersting for the player, while also making AI beastmen a more enjoyable threat than they were in game 1 by increasing their staying power.