Step it back to their base classes, MMO stereotypes and lore reasons:

Nin + Bard / Rogue + Archer = your MMO leather scout classes depending on whether you like stabbing or pew pew. MCH, which was added with HW, simply got lumped with Bard gear for simplicity.

Dragoons / lancers = your MMO not quite a tank plate wearing DPS.

Pugs (hue) / MNK = your naked or sometimes clothe wearing MMO fist fighter.