Ah, but that's the thing: the kids aren't half-exiles, it's just that its extremely easy to recast them as half-exiles once they reach adulthood if the local authorities decide that they want to do that. Because they often aren't treated particularly fairly, all the chiefs need is to get them to lash out once when they're young adults (like that's uncommon) and then hit them harder with punishments than is entirely necessary or even recommended.
There's basically a lot of stuff that is made to work most of the time, but that also has a malicious usage that not only has immediate consequences, but also has long term compounding effects. Like, thus far the People have managed to avoid some of the worst effects of polygamy both because a man having more than two or three wives is almost unheard of, and even two wives is quite rare and mostly among the most politically active classes for the purposes of securing alliances. Communal property has helped a lot by not producing an unreasonable number of heirs to divide property and create conflict points, but the Stallion Tribes are honestly going to be the nucleation point for a number of social problems as they are the spearpoint of interaction between the People and other cultures. The People don't really do any wife stealing, but their relative strength, success and theories of war and justice means that they tend to end up with a population lacking most of its adult males in need of resettlement, and the social structures to support large numbers of children as a group, so there is an obvious combination of good traits leading towards a long term disaster.
Since it would be an in-universe concern, the next few kings may wish to figure out how to integrate the March sooner rather than later. *cough**cough* Admittedly, figuring out how to do that is one of those flailing in the dark things currently.
