Archetypes are an interesting beast. They are the primary pathway in the game to taking on feats and features from other classes, via Multiclass Archetypes, but they're a lot more than that, too.

One of the things they're leveraged for is class variants. There's not a wealth of examples in this category, but it's kind of tantalizing. This is where you find PF2's equivalent of the Wild Mage, the Wellspring Mage. It's also where you can straight up just choose 5e style hybrid casting, with Flexible Spellcasting.

But the real core of Archetypes seems to be turning background flavour into defined game mechanics. Here, OP could make a melee archetype that could apply to the Fighter, Barbarian, and Monk classes, providing depth of fighting style and role to this society without needing to develop independent subclasses for each of them.