Sure, Death Touch is high level with a high AP cost, but that's fine. The build plans for Witchcraft 4, and the Inquisitor gets quite a bunch of AP per turn. The AP cost doesn't matter much because the cooldown means I can't use it that often anyway.
I like Vampiric Touch for this build because A) the Inquisitor doesn't have a lot of direct damage spells, B) It does damage that can't be resisted - making it more useful on frozen enemies than Burning Touch, for instance, C) It provides some healing for the Inquisitor, letting them use their other healing spells on the other party members, D) What else am I gonna do with all my skill slots?
Later on, I'll try to record another big fight at about level 11 or 12 and show how the build works in the mid-game.
I'm less sure about how well it'll work late-game when enemy resistance to status effects is pretty high.