Afaik this is correct.
You have unlocked most (all?) archetypes from the beginning, but you unlock other items which are not part of "Archetype sets" through challenges, achievments and the like.
There'd best be a decent amount of non-archetype pieces to unlock... not sure why but I was under the impression that some Archetypes would be unlocked through playing, without that there's less a reason to keep playing Brink's already small campaign. Unlocking stuff is half the satisfaction!
EDIT: remember the Qore preview? Where that annoying woman ("BRINK IT ON" :banghead: ) says something along the lines of "if you see a guy with cool duds, steer clear - he had to earn that look".