obviously gems are expensive now compared to the start since raids released people got more items worth upgrading and everyone is trying to get gems now, this is not a crazy unknown phenomenon, it happens on every raid / tier release.
now looking at the ladder it is quite obvious onyxia would not be able to sustain a healthy arena ladder or environment on their own, i do not know what players there are doing but playing pvp / arena is certainly not a daily activity so how would this realm survive pvp wise?