There is every sign that -- if Harry hadn't had the Spear to pull out at the last minute -- Ethniu and the Fomor would have won.
But without Ethniu would the Fomor even of had a chance? Or rather much of a chance? She was their bad ass terror weapon with a very nasty eye, without her the Fomor were really quite run of the mill in the Dresdenverse.
Funny how Harry stumbles into things, needing to face the Senior Council? Make a bond with the island with no clue of the repercussion of what he is doing, wakes up a couple of books later to discover that he is Warden of a Prison of some of the worst monsters his world has ever seen... And also finds out that he has the power to incarcerate more monsters if need be with in range... Pretty handy for controlling a Titian running amuck.. Reluctantly goes down into the security vault of Hades because Mab owes Nic a favor, happens to find and recognize the Spear of Destiny and a couple of other useful trinkets, which were very useful in dealing with a very nasty Titian a book or so later.. Turns out it was Harry verses the Fomor and Harry verses the Titian, no Harry, the Fomor win.. However I don't think Harry realizes that just yet, at least not fully, but the White Council realizes it, that's what has them pooping their pants and wanting Harry dead.