So when thinking about the Grazelanders, it is perhaps best to think of them as a duopoly headed by the Feathered Horse Queen. That means two groups:
Semi-nomadic horse herders. These folk call themselves the Pure Horse People but would be barely recognizable to their distant kin in Pent and Erigia. Others call them the Pony Breeders. They raise and defend their horses, moving them around from pasture to pasture, supplemented by hay grown by the farmers. They are provided with additional foodstuffs, crafted goods, and so forth from the towns and villages, but in amounts set by the Feathered Horse Queen and acceptable to both groups. They worship Yelm and Ernalda.
Farmers and townsfolk. These folk are Orlanthi farmers, crafters, and merchants. They also include the Humakt cultists, who are the ferociously loyal bodyguards of the Feathered Horse Queen. They farm their fields, make craft goods, and run the markets – and give a percentage to the Feathered Horse Queen and to the Pony Breeders. They worship Orlanth Thunderous/Barntar and Ernalda, as well as the other Lightbringers and Humakt. Many have commercial or even kinship ties with Tarsh and Sartar.This sort of co-dependence between farmers and nomads was pretty common in the real world. Farmers cannot easily become Pony Breeders, but are not slaves either. Disputes between the two groups are resolved by the Feathered Horse Queen who is above both groups, as the living incarnation of the Earth Goddess. The Feathered Horse Queen dynasty is closely related to the Sartar Dynasty and since 1605 or so to the Tarsh Dynasty in Furthest.
The Feathered Horse Queen is very much the ruler. And she protects the farmers from the Pony Breeders AND the Pony Breeders from the farmers! The local Humakt cult is pledged to her service (likely as part of their initiation rites), and she controls the fertility of the lands and the herds. Life served by Death.
There are in total about 40k people in the Grazelands. 18k are Pony Breeders, 18k are farmers, and 4k are urban townspeople.
It is also worth keeping in mind that Grazeland society has been half Orlanthi farmer and half Yelmite horse herder for over a century or more. Both cults compete for the favour of Ernalda (the Feathered Horse Queen).