And regimented/stratified society as we understand it has existed for far less time than it hasn’t. We could go for pages and pages on this point and philosophers often do,
maybe you would find some of the writers that were mentioned above by @damalsk interesting on this point, though i will not link any as i do not think it’s the place to be linking political and philosophical texts. 
t’s really not here nor there because on a micro level, as in the amounts of people we’re dealing with wrt people within the game, will diverge massively from general rules that could or could not be applied to humanity as a whole.
I agree though, there would still be a lot of people behind them, especially the better off or comfortable middle classes who have lost alot, as well as just the opertunities that see safety in the resources they can (or at least claim to be able to) provide.
With this faction i am attempting to deal with those who might have been critical of the Old World before it’s fall and those who might have found themselves in a far better position and gained massively since.
I would love to see someone expand the Old Guard past a couple of guys in the Evac Shelter, but i don’t think it’s for me as i’m personally far to far away from that point of view to write it even close to well and i have no idea what it would begin to look like.