Actually, scrap scrapping the vampires. I can't think of anything better. I have a better social order though. Same backstory, different set up.
Top to bottom:
Chief vampires: 2 people
Noble vampires (children of vampires and pre-tribal vampires): 1/1000 people, roughly. Can vary.
Chosen vampires (Chosen elevated to vampireship for good service): 1 per 200 population
The Chosen (Keep the peasants in check (No other tasks); normal, unbitten humans): 1/5 of the population
Peasants (Through propaganda, magical suggestion, and a lack of education, kept from the truth; they are basically slaves): Rest of the population.
Blood-slaves (Virtually mindless drones, for tasks too dangerous or menial for the rest): Varying amount. Never more than 1/10.
Chief & noble vampires are powerful- but not strong enough to take on an army. Together they could stand against ten men per vampire, perhaps. They are theoretically immortal, but as the body deteriorates, more and more life-force is required to sustain it. Vampires are not undead- they just don't die of old age. If they did nothing all their lives but drink blood, they would be immortal. But wear and tear takes its toll, and eventually the vampire must consume more than an hours worth of human life-force to survive an hour, and they die. A typical vampire can live 300-500 years before their body damage drags them down. Vampires have limited natural magic; natural blood magic, which facilitates their other magics; the magic that allows them to leech life force, their magic of loyalty, making the bitten loyal to them in varying amounts (can be taken to the extreme- see blood slaves). They can also transform the bitten into a (chosen) vampire. Vampires can also learn other magic. Careful study allows them to leech magical power as well as life force from their victims, making them powerful mages. A common spell they indulge in is metamorphosis to a [bat].
Chosen vampires are weaker than Noble vampires. They have lived as men for some of their life, and so their powers are diluted. They are not capable of withdrawing life force (and, if mages, magic) from their victims with the same efficiency as noble vampires. Nor can they instil the same level of loyalty as nobles (and are thus not capable of creating blood-slaves).
Chosen are those humans who willingly aid the vampires. They are treated well. Housed in the city center, in real housing. They are also constantly reminded that betrayal means blood-slavitude, and good service means a chance for vampireship. This means that almost all are truly loyal.
They police the streets of Bloodarch camp, armed with the best weapons. They receive education, and do those tasks that require a degree of real skill, but to menial for the vampires to do. When peasants flee, they chase. They spread propaganda, and provide a constant reminder of who's in charge to the peasants- not you!
Peasants are the working class of the Sentivore society. They are uneducated, knowing no more than they need to to do their jobs, which is usually not much. Most of them have the two red marks in their neck indicating their position (biting in the neck is not required, but Sentivore dress code require bear necks for a reason. No peasant will ever pass as chosen (or vampire, but yeah, vampires. Big teef, right?)) They will never rise above their station. Of course, actual complaining is a lessened by a number of factors- the constant propaganda, the constant watching eyes, and the slight, but ever present magical voice in the head saying; ah, its not so bad.
Not that they never revolt. But there are ways of dealing with that.
Revolts happen. How often? About 4 times a year, on average. The revolters always flee the city. Most of the time, the chosen and a few vampires go out, hunt them down, catch them, and then they are made into blood-slaves. However, once a year, a revolt succeeds, and the fleeing people are never seen again. Well, sometimes they return as a small army, but they are always crushed. This is on purpose. If peasants think that fleeing the city has a chance of success, they are less likely to stay in the city, causing collateral damage, or worse, inspiring others to help them. Worst case scenario, they all storm the center, and everyone dies. So once a year, a small revolt is put under fake pursuit, only to be lost. All that is required for this most effective prevention of mobs is for the fleeing peasants to be small enough in number that the Sentivore's 3 kids per family plan can deal with them. Food inefficient, maybe. (Give me a food penalty, or something) But keeping the amount of fleers down is the task of undercover agents who infiltrate and betray the groups. Once found out, the group usually flees. Most groups never plan to do anything but flee and 'come back for the rest later'
Being a Blood-Slave is a fate worse than death. A noble vampire can (at a cost) make you so loyal that your real personality is lost, and you become hardly more than an extension of their body. Blood-slaves are used to do those jobs so dangerous that no sane man would do them and not believe his fate utter slavery. Deadly work in mines, back-breaking construction, front line against rebel armies, they do it all, without complaining. They can't complain. This deadly work is also handy in that it removes the strain on the master vampire, as the maintenance of blood-slaves is tiring, even dangerous in cases.
Blood slaves is the chief punishment in the Sentivore legal system. Recaptured rebels become them. Criminals become them. Disloyal Chosen become them.
I can see that working. I really can't think of anything else which isn't done already or unoriginal.