So, you just want a compendium of rules for various setting specific things? I don't think I would like that, much prefer setting specific rules to stay in the setting books where they will be easier to find.
Sure, I'm going beyond what is explicitly stated, but I'm not just making things up. I'm following the logic of exactly what it says and assuming there are not caveats like "this only applies to adults over the age of 21".
Well, here’s the thing, you could just as easily look at all the text you used to suggest that they’d be brutal to their young in order to make them stronger like the Spartans, and instead go the other direction. They expect the young to contribute once physically able, like practically every society in RL history until less than 100 years ago, but don’t hold them to the harsh standards described in the “survival of the fittest” section until they become adults. But for some reason you’ve gotten on a track where you seem to need to make them out to be as grim dark as you possibly can in order to convince us that they’re dark.
You also could go the other way on the details of leaving behind the “weak” and injured, as I’ve already described. The way you’ve been going
isn’t a necessary extrapolation, it’s just one possible direction among many.
Heck, all I'm saying is that their RAW lore is terrible.
Their lore is bad in a few parts. As I said at the beginning of this exchange, you can drop the worst couple bits and they work fine. The competition, focus on accomplishment, fair play, need to be free to wander, feeling at home in the most remote regions of the world, being most at home in a world where survival is actively difficult, etc are all interesting enough to hang a culture on.
Even leaving behind those who can’t keep up doesn’t
have to be
brütal and grim-dark. Literally just change it to a scenario where the infirm and old and too injured to keep up and whatnot are given basic supplies and sent to live with the lowlanders, next time the tribe is down that way. This is still harsh but not brutally so, they just exile you if you cant keep up, but they do it in a way that isn’t likely to kill you.
Or create clan-holds where the tribes and clans come together seasonally to trade and share news and arrange marriages, and seek council. The disabled, infirm, elderly, etc, live there, and are still expected to excel at something, to keep as fit as their body allows, and to provide utility to the tribe/clan.
It’s a small change overall, but makes them a less ridiculous society, while keeping what makes them unique and interesting.