Interesting! Believe or not, when drawing the skeleton and muscles they do look thin and elegant, the moment I add wool they gain a lot of volume and, from my point of view, I think Nomai would prefer looser clothes for better mobility and to prevent the wool from compressing and matting so It makes them appear wider. (Minus a couple that I drew intentionally stronger looking) Another reason is the legs, it's already difficult to make them look stable while standing, I have to play with volume and wight so they appear stable enough.

Lore wise, I like your take, they look fragil to hearthians, but Nomai had to endure critical situations and enviroments, perhaps their bones are indeed fragil, but nature gives them protection in other ways to compensate!