Well real mage Build in general can work even in endgame but take much more effort. Iam Atm using a DarkFlame Mage where i focus on together with other stuff on Consuming Embers empowered with the Force of the Occult(Aether, Shadow and Sacred Dmg) that deal a decent amount of dmg. Saddly i never read "the Dresden Files" so i have not a clear idea what you look for.
you wont be killing with Consuming Embers alone in higher Ranks thou. My DarkFlame Mage uses Anomaly, Solarfall, Tear of Etheliel, Aether Jump and ofc Consuming Embers. Wearing Heavy Armor Head+Chest for Salavtory Anchor, Rest Bruiser Gear with focus on Toughness, Cost Reducution and Occult-Dmg.
if you are intressed i can post my Current Build on Wolcen-Universe for Review.
What it can do sofar: Running Expedition Rank 163 without a sweat and lays down devastations in resonable time to bosses and packs a like. Didnt Try 187 yet since i dislike doing such Stuff while iam not "ready prefectly"