I think it makes much more sense on Dragonhunter. DH's profession mechanics designed to benefit allies, while WIllbender is an individualistic Thief-like elite spec.
In a perfect world, it would have made even more sense for the Dragonhunter (archer/trapper) to provide quickness, and for the Firebrand (mage/knight with a lot of spells) to provide alacrity.