Yk initially I'd kind of liked the idea of someone sandborn being assigned as a vargard being seen as a bit odd but as I was mulling smth earlier the mentality did a full 180
I'd previously been running mostly with the logic of nobility of various ranks often being prioritized for higher military positions. Like, if you were from a family of lower standing, instead of aiming to be an admiral or nemesor, you'd likely aim for lychguard or vargard, and likewise those positions would often be more freely assigned by class first, skill second (unless the disparity was too much to ignore).
But then I thought about it, specifically thinking about the adoption AU, a conversation Zahndrekh has with Oltyx, and I realized 'maybe it actually makes way more sense for a vargard to be sandborn or otherwise significantly lower ranking because they'd probably have nothing to gain through betrayal'.
If an overlord has a vargard who's from a pretty prestigious bloodline, it's easy to imagine they'd have plenty incentive to usurp them, and possibly depending on the dynasty's own beliefs around that sort of thing, would be seen as fit for the throne if they pulled it off successfully.
I don't feel like they'd be so gracious with a sandborn soldier elevated to such a rank and then using treachery to attempt to pull themself higher.
Vargards are kind of unique, aren't they? They don't just hold a military role, they're essentially an extension of their master. Lychguard captains seem to be a similarly equivalent military rank, but vargards are the second in command both on and off the field. They don't outrank other nobility within the court, but they do seem to stand almost alongside them, and they can command them when on their own masters orders.
It seems like the type of position someone could really take advantage of, especially if they have the breeding to be more easily endorsed by the court should they so choose. Especially someone already raised with some measure of entitlement engrained into their psyche.
But sandborn soldiers are raised to believe their sole purpose is to serve their betters, and that there generally is no place for them anywhere higher in society, so what would they have to gain? Perhaps in some unusual circumstances it does work in their favor, but I'd be more than willing to bet it would otherwise not. That, on top of the improvement in living conditions with the role alone would likely be seen as plenty to fully ensure the desired, unfailing loyalty.