Possession is for damage absorption and Chaos resistance.
Master of Death’s only use is the extra OA. +12% OA on an Exclusive skill isn’t attractive to me.
Aye, the Dirge of Arkovia pet 
And between the Relic & Amulet change + untransmuted Blightfiends, build lost a lot of damage from its original counterpart The Rawr God - Pet Cabalist
Plus I didn’t bother trying to keep pets alive in my run, so they lost their blessings, which further increased the clear time.
And as someone who has never done a Crucible Speed run, I can tell you how to do it:
Spectral Wrath doesn’t really do much here due to fully converted Blightfiends + 80% physical to poison on the rings (max roll), but it should still provide some extra damage due to phy RR (Skeletal Servant & Talon), so feel free if you wish.
!7/16 Reap Spirit gives you 2 of them. They do decent damage.
Rotation? what rotation? 
We don’t do stuff like that in FwuffyLand. We just roll head on the keyboard.