Still sounds like a case of "doing it wrong." I'd still ask that clerik to come up with a better description of his effect than "let's see what the dice say" before rolling the dice. Does "ALL OF THE HOLY DAMAGE
" mean he's calling down beams of divinity from the sky? Is he channeling kamikaze angels through his holy butthole? Is he spitting sacred incense breath that explodes on contact with demons?
You have to have your story in place, especially when the Fumble dice pop up, because explaining how the butt angel delivery got messed up is way more satisfying than just subtracting 3 from the end damage.
That does bring me to another problem with the current Arc Fire and Area Effect rules - what if I hit a bunch of enemies with the same d6 of Damage, and it only Fumbles on some of them? Do I handle each Fumble separately? I'm leaning towards saying that any dice that are multiplied by an Arc or an Area lose their SuperNatural qualities, because that makes other stuff easier as well (Lasting Effect dice, for instance).