This should be simple enough, current GLDs and MRDs can compete with DPS of low levels. Adding a DPS based job at level 30 would be nice as well allowing these classes to not be forced into tanking as it is rather overwhelming to newer players.

GLD job could use a second sword in off hand to allow for more damage and change Emnity generating attacks to get higher damage or even reduce emnity.

MRD job could use rage for extra damage rather than HP and Eminity bonuses. Again Emnity generating attacks would have to shift with new job to increased damage or the like.

Adding these jobs would increase flexibility of MRDs and GLDs and allow tanks to get a feel for new dungeons before running them without having to level another class.