Long story short: my story has magical humanoids (known as "immortals" due to their immunity to old age and disease) existing in secret on mostly-modern-day Earth as a 1-in-1000-humans minority. One of these species is vampires, and they are arguably the dominant immortal species on earth. One of the reasons why is their ability to swiftly replenish their numbers by turning humans into new vampires, instead of having to have more children like most other species are restricted to (although to be clear, in this setting vampires can do this too).
An important thing to note about this is that there are four degrees of magical potency a human or immortal can possess, called arcana. While this has no impact on humans while they are humans, as an immortal the higher your arcana, the more of your species' powers and the fewer of its weaknesses you possess. In ascending order of power these arcana are: gamma, beta, alpha and cambion. While in those who were born immortals these arcana are inherited based on what their parents' arcana was, for those born human it's entirely random, with your parents' arcana being irrelevant. Humans have a 60% chance of being born a gamma, 30% a beta, 9% an alpha, and 1% a cambion.
And the reason this is important is that a human can only be turned into a vampire if it's done by a vampire who is at least one arcana higher than the human is. Meaning that it is impossible to turn a cambion human into a vampire.
Due to this, cambions are not just the most powerful members of the species, but they're also the rarest and hardest to replace, and as a result most organized groups of vampires go to great lengths to keep their cambions safe, leaving the most dangerous tasks to the lesser arcana vampires who can easily be replaced in a night or two.
However, something interesting occurred to me about this system:
Higher arcana are indeed significantly rarer in humans than lower arcana are, but thanks to the fact that there are ways to tell what arcana a human is, that's largely irrelevant. The highest sirable arcana, alpha, may only constitute 9 in 100 humans, but as I said earlier immortal beings as a whole, let alone vampires, constitute a mere 1 in 1000 humans. Meaning that even in areas whose immortal population is 100% dominated by vampires, there would be 90 alpha humans to every vampire. So logically, vampires would be spoiled for choice as to who to turn into a vampire even if they excluded all but those of the highest arcana they are able to turn.
For this reason, it seems to me that any organized clan of vampires with access to cambions would have no practical reason to ever sire non-alphas into their ranks, and betas and gammas would be almost exclusive to smaller groups that have lost their cambions and only have alpha or perhaps even beta vampires to turn humans with. Sure, there might be vampires who would want to make betas or gammas into vampires out of emotional attachment to them, but it still seems like betas and gammas would ironically be an overwhelming minority in cambion-run clans, despite technically being the more likely result if you turned a human at random.
I don't particularly have a problem with this. Those lesser clans would offer plenty of opportunity to explore the lives and the obstacles of vampires of lesser blood. But I want to double-check my logic a bit, and see if I'm missing something here.
Given the system I have established above, is there any practical reason why a vampire clan wouldn't fill its ranks with the highest quality of vampires they can make?