It's worth remembering how the Unravelling does that: it splits the person into two people, one of whom does stay with the God, unless the person in question pull a Dany and convinces their new self to work with them.Sure, Godsbane sounds like one hell of an effect to drop at enemy cleric(s) - but an Unravelling can cut someone clean off their Deity.
So it's not always that amazing.