Merge the factions. Alliance and Horde players can group and raid together. For PVP it’s still seperate and Alliance and Horde questlines and cities are still seperate.
I guarantee this would fix the imbalance. The imbalance right now is because it’s easier to find a group on Horde side.
This would let people play the side they prefer but still allow them to find a good group to raid/mythic+ with easily.