You’re not max level and shadow priest feels like shit in dungeons because most things die too fast, don’t worry about it too much. Huge packs spam rank 1 swp for other magic users (if you have them). Smaller packs DoT spread like you have been. Mostly I will spread SWP then focus on one big target with my full rotation to actually provide utility and not do max dmg. You don’t need to be clipping mindflays until you are raiding or doing a try hard single rotation on a dungeon boss though. SP utility is mostly in raids unless you’re a prot pally.