While playing a Lich, I noticed that the cast speed for Spirit Plague seemed awfully low considering the amount of increased cast speed for that skill. After a lot of puzzlement and some testing, I realised that the Conductor of Plagues node effectively halves the cast speed for the skill because it appears to alternate between casting Spirit Plague and casting Spread Spirit Plague (the name I’m giving the implicit “skill” added by Conductor of Plagues).
At least, that 's my understanding. I recommend improving the description of the node to make it clearer that the node effectively introduces an extra skill that alternates with the main one. Or perhaps a “additional information” block that explains to the player that they will see a big reduction in apparent cast speed.