I also tested the combination.
Slash : Remove gcd from slash but increase it's cooldown and push it's damage slightly. Right now, you only use this skill because of the Hearts Death debuff. This would give the class a useable spammable.
Psychic Warrior (499868): Reduce the cooldown to 2min, remove aggro increase and damage taken decrease and let the skill increase your magical damage and dark damage by 40%. Reason behind that is, that skill as a skill with 5min cd is useless. Knight/Warlock e.g. has a skill with 1,5min cd that increases dark,light and pdmg by 40%. Even the elemental catalysis of the Mage increases mdmg and area damage and you can use that skill 2 times (with ISS).
I completely agree. The combination only has Slash as an rage attack and it would be helpful if it were pushed. The suggestion for Psychic Warrior is good.
Death Heart: Although this is a great support skill, in my opinion, this should be changed to a self-buff (like you did with Earth Pulse od Mage/druid) and (maybe) increase the damage by 10% or so. This skill supports not only other Warlocks atm but a lot of other pdps. Since the physical damage formula works differently than the magical damage formula the 30% dark damage increase at least doubles the physical damage hits. (from what our pdps told me).
Unfortunately I have to agree here too even if it breaks my rogue/warlock heart
Of course that´s just my opinion.
Kind regards