RDM is restricted to cloth armor and scale armor whereas BLU gets most cloth armor but also rogue armor(encompasses light armor for THF/MNK/DNC/COR/BRD/NIN). So BLU can use things like Ocelomeh/Toci's/Homam/Thaumas and RDM cannot. The tradeoff is that RDM can use Rubeus(meh), Anhur, Hyskos, Nares