As Kalimac has stated, the Armoury System is built around the fact that weapon type determines class - in fact the term 'class' is something of a misnomer, in that they're not really a class at all but a set of skills connected to the use of a type of weapon (hence why they're properly called 'Disciplines'). It's also the reason why there's no specific 'class' sections on this forum - they're based on the role they play in a party. Hence it's pretty impossible to give different weapon types to classes as it would completely destroy the whole concept.

Personally I think there's nothing wrong with the Armoury System - I would just like to see classes given more relevance in situations where it's better to not have a Job crystal connected.