It seems to me that Instakill ability of Sister's of Battle Banner or Revenge have slight oversight.
It's allows inta-kill Nurgl's infestations. Which allows for pretty hilarious abuse of putting perks into defence trees, boosting speed throught miracle or equipment, and then simple run throught all enemies, target select infestation, use banner and then run to the next. The only thing that can stop the player are traps, most of which the player will be able to outpace anyway. The minimal time of destruction of all three hives in Nurgl's Infestation, after reaching first, becomese 1 minute 40 seconds and can be reduced even more. And it is for solo player.
Even with no reward for killing enemies, it's still creates disadvantage between people who noticed this and not.
I also not sure if it can down the Warp Gates too.