Dragonknight spells

Nebell

So I've been playing my dragonknight with mixed physical/spell damage. My weapon damage is 160,however my spell damage is half that, 80. Does that mean that spells like lava whip do less damage? It's fire damage type, which should be affected by spell damage?
If so, how do I increase spell damage as a heavy armor, 2h dragonknight?