I've done some math on the idea of keeping 100% uptime on Fracture with 100% Deliverance uptime, and things seem to point to Fracture being a slight DPS loss if kept up during Deliverance. It still remains an increase in Defiance, however, and the ability to swap into Deliverance for TP gain makes it much less detrimental to use while MTing. Of course, if a boss is about to become untargetable or you need to step away from it for a moment, it's a good idea to stick it on no matter your stance.