For conceptual reasons I'd still put it under Destruction, not only because it spreads the spells pretty evenly, but also because Dispel literally destroys magic. It's what it does. You can destroy buffs on enemies or debuffs on yourself. It can be used aggressively as well as defensively, e.g. dispelling an enemy's summoned creature. Same as killing it, really. Detect life (and other things, possibly) goes under Illusion because it affects your vision. Resist and Telekinesis both affect you or the world around you. (Telekinesis is supposedly a straight ripoff of Dark Messiah. I hope the rumor is true.) Soul Trap goes in Conjuration because it deals in manipulating souls. Spell Absorption belongs with the other absorption spells, hence Restoration. Dispel is really the only truly destructive one among them. Destruction is not just about direct damage, it's also about destroying the enemy's defenses or weakening them. It makes sense for the debuff spell to be a part of that.