Remember what Melindra said ? She said that eiden and eleya would have been almost called couples if it was not for one being from earthern whereas other from magical. How can eiden be a spirit then ?

Also , Arraka herself was responsible for the banshee's banishment , not eiden. She didn't even know eiden until the still winter. Eiden is about 600 years old whereas Arraka is more than 1000.

My theory is that Eiden is currently wielding the Magium and he is the main organizer of this tournament and his motive is to wipe out all the powerful mages... He has already told us what his motives are.. So this seems like a better possibility that he organized the tournament just to cause mere bloodshed.