I personally want to be able to tank as a RDM whenever the situation might call for it, for example the tank has too many mobs on them at once and nobody else in the party is situated to tank, like with most parties you got mostly DD but they arent really equipped to tank, RDM can in most cases tank fairly well after level 34 with flash and stoneskin, and even better with Utsusemi:Ichi/Ni and with the right gear