FB -> RB is 2 GCDs. Fracture is 1. Fracture does damage, keeps enmity, and is a DoT. It is literally your best option for holding hate on multiple mobs at a low level in every possible way. I don't know what you're trying to counterpoint here - you use it to do damage, and damage is enmity. Enmity modifiers do matter, yes, but you don't NEED one on Fracture for it to be the superior option in every possible way for low levels.