If it helps, just pretend that Defiant Challenge is Conviction.
But, really, the idea is that you grab and hold aggro by dealing damage. You shouldn't need to be spamming threat leeches, because you have innately higher threat than everybody else in the fellowship. If you lose aggro, DC pulls it back for you. If that sounds really simple, it is, because you're supposed to be spending most of your brainspace on maintaining a defensive rotation.
Cainwen Ciaphas, Captain of Crickhollow, HERO OF MIDDLE EARTH!!!
I will not be pushed, filed, stamped, indexed, briefed, debriefed, or numbered! My opinions are my own!