You are neglecting resistances, Conditioned Body and Indomitable Will. A high vitality may well make up for lower resistances, though, especially for a ranged character early in the game (when most opponents are melee). I boosted intelligence a bit in D2:ED with my warrior. In DKS with a ranger I didn't put any stat points into intelligence, and only ran into a couple situations where a higher Indomitable Will would have helped (with stun arrows).
I have not played a mage character, but just checked in a save at the end of D2:ED, and intelligence doesn't effect Magic Missile damage.
There are some more details on stats in the
Character Optimization topic (which you've probably seen already).
Welcome to the forum.
