pyromancer
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n. One that performs divination using fire.
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n. One that has a magical ability to conjure or control fire.
Grim Dawn’s Pyromancer weaves flame into devilish sigils (Sigil of Consumption -> Destruction) and hellish creatures (Summon Hellhound) whilst bolstering both with arcanery (Flame Touched, Vindictive Flame) and coupling the above with pyrokinetic armaments (Grenado, Canister Bomb, Thermite Mine).
That your expectations of high fantasy do not align with the victorian-era eldritch horror story of Grim Dawn’s setting is a you problem, not one for the game to address.