Its job requirements as a jack of all trades requires it to be able to do everything to an acceptable standard while not going beyond those who are designed with the specific capabilities to melee awesomely, for instance, we are not meant to beat a WAR, DRK, or SAM, however we can come close to a BLU, THF, or NIN, and still be within our job description, we will not be top of the DD charts. The thing that is harder to balance about melee is the fact that unlike healing, where we are 3rd (WHM>SCH>RDM>PLD) or nuking where we are 3rd (BLM>SCH>RDM>DRK) melees have a much longer list of jobs, and in the end, all jobs can truly melee to some extent, so the question becomes where does one draw the line for RDM? In truth, even if you gave RDM the light DD sets I ask for all the time it would boost RDM's damage by enough to put it closer to the light DDs but it would not surpass them, most of them either have better WSs or better traits/abilities which let them surpass us either way you go about it, but it gets us closer, as a jack of all trades, that is our goal, to be following behind others enough to be of use but not enough to be stronger than them.