I'm level 47 Nightblade and cannot beat the Lyris Doppelganger, not that one of the three bosses in the Fighters Guild quest, and also not the Harvesters you have to kill during the biggest quest in Coldharbour.
Without being able to cast either area effect spells or summon anything, you're pretty much forced to either start a new character (preferably a Sorcerer) or to simply unsubscribe (which I consider now).