The big issue with horde factions in the game is that they're anything but.
Horde factions' gameplay tends to encourage the use of a few elite stacks while not really encouraging the use of multiple armies. The most effective tactic, and one with little to no drawbacks with these factions is a deathstar of multiple armies all reinforcing each other.
In a word, horde gameplay is boring. They're boring to play as and even more boring in the hands of the AI.
I would like to propose that horde races be overhauled so that they both have a unique flavour to their gameplay, as well as some places to protect and rebound from in case of losses.
I made a thread detailing how this could be done for historical hordes here: " https://forums.totalwar.com/discussion/217360/making-better-horde-factions-especially-nomads#latest
But for Warhammer, I think that the following system should be used:-
1. Horde factions should get settlements. Beastmen herdstones and Chaos Rifts respectively are lore appropriate bases for these factions. These bases would largely act as normal settlements with the exception that they wouldn't have any sort of economic or garrison buildings.
2. These bases would be unable to get walls or enhanced garrisons, being entirely reliant on their field armies for protection.
3. These bases would serve as both recruitment and replenishment centres for horde factions, field armies wouldn't be able to recruit outside of these areas, not even through encampments.
4. Horde factions would have little to no economy, being almost entirely reliant on raiding, sacking and battles to gain any money beyond their starting income. They may get some token income from their main settlement building, but this would never exceed 100 gold at best, which would require them to rely on raiding instead of their settlements.
5. Horde factions wouldn't pay the supply lines penalty for additional armies, encouraging the use of multiple armies instead of a few elite stacks. Especially since they would also need to protect their bases.
6. Hordes would also rely exclusively on these bases for replenishment, with replenishment being reliant on corruption and main building level.
I think that theses changes would make horde gameplay more dynamic and more interesting to face by both giving them something to defend while also giving them bases to rebound from. On the other hand, these factions would also need to be actual hordes with multiple armies due to the defenseless nature of their bases.