Grinding is a fact of life in MMOs. Having said that, I think the drop rates on the mirror and the mounts are too low to serve what I imagine their purpose is - getting hardcore players to farm said content, thus keeping the dungeons more active for newer players to find groups, as well as to improve the odds that the newer players succeed by having experienced players assisting. The problem is that the items are so rare, that most hardcore players don't bother, negating those benefits.

If on the other hand, they just wanted to have something extremely rare for the sake of having something extremely rare, then they succeeded.