Well the Strong Tribe are the only ones who have the armor, it's the specific technology/bonus that they got when Ialu founded them as an order.

The Cimex and Dyun failed at killing the dragons and I doubt ordinary humans would fare much better. Maybe they've slain the odd few that attacked villages, but I doubt anywhere near as many as the Strong Tribe. Ialu has personally slain most of those dragons, with the help of his hunters that have their special Wi.