The current form of Invocation is this:
Invocation: Refreshing Corruption, Immolate, Curse of Agony, Unstable Affliction, or Siphon Life when it has less than 6 seconds duration remaining will cause you to deal instant damage to the target equal to the spell’s remaining periodic damage.
The main reason why it’s garbage is because Shadow and Flame is so much better in every conceivable way for bassline dps.
Shadow and Flame: Your critical strikes with Fire and Shadow spells increase your Fire and Shadow damage done by 10% for 10 sec.
With the recent release of Pandemic, this rune, when paired with Shadowflame, is just so much better, because it’s a flat dps increase, and you don’t have to worry about watching your dot countdown.
Grimoire of Synergy: Recite from a dark tome, granting damage done by you or your summoned demon a 10% chance to increase the damage done by the other by 10% for 15 sec. Recitation lasts 30 min.
This rune is garbage for the same reason as Invocation, because Shadow and Flame is just too good, for both dps and tanks.
However, I do have an idea on how to fix both runes, without nerfing Shadow and Flame.
First, Invocation. The current iteration of Invocation is just not a good idea. No one wants to be watching their dots countdown, so please don’t try and make it work.
Here’s a better idea:
Invocation: The periotic damage of Corruption, Curse of Agony, Unstable Affliction, or Siphon Life has an 4% chance to create an Invocation of Shadow on the target, increasing Shadow damage by X amount.
This is much better better for Affliction Warlocks, and this way they don’t have to rely on Shadowflame to increase their damage, instead allowing them to use Demonic Knowledge.
Second, Grimoire of Synergy should be tuned for Warlock tanks and not have anything to do with damage at all.
Here is what I suggest would be better:
Demonic Synergy: When in Metamorphosis form, 50% of all threat generated by the Warlock’s minion is instead given to the Warlock himself. When not in Metamorphosis form, 50% of all threat generated by the warlock is instead given to the minion.
This way, Warlock tanks can use their tanking pets as a secondary form of threat generation.