It's kind of like giving a 2005 ninja ragnarok, yeah all the "special" people would do it, but we all know that putting a Heavy weapon on a Light job is just /fail. Facepalm city.
This is pretty much the issue. RUN's issue is that it completely lacks in decent sword options as well as any form of native DW (or attack boost).

Here's the issue with GS guys, it absolutely requires large amounts of attack to perform well, this is why DRK and WAR (prior to delve) could put out so much damage with it. As RUN is totally lacking of this trying to use a GS is a bad idea. There ~is~ a niche that needs to be filled now that Twilight has lost it's luster, the niche of a DD that deals non-physical melee damage. The closest we have now is enspell'd / FS MNK's or Req / Sang spamming BLUs.

Now give RUN two very powerful swords and hopefully some form of MAB (tier 1 is fine) and they could spam Req / Sang while also dealing magic elemental damage and thus become a much desired utility job.

RUN is not a tank, will never be a tank, and was never a tank. Those who think it is or will be don't have the slightest clue what a tank is or what's involved with being one.