In the context of Liches, how useful is healing effectiveness ? It says it doesnt help regen, leech, hp on hit, and potions. Only skills benefit from leech. The lich has 3 skills which can directly heal a player (pretty sure?) aura of decay, drain life, and rip blood. So if you’re not running one of those, would healing effectiveness be largely useless? Or does the lich passive bonus, 1% damage leech, actually benefit from healing effectiveness?
The 1% Leech from Lich’s Mastery Bonus and the 5% Leech and another 5% Leech on hit from the passive tree are all considered leech, so it does not affect it.
Also Drain Life is considered leech (it does say that in the tooltip).
As you already noted Aura Of Decay’s Absence of Life and Rip Blood’s health from blood orbs is considered healing.
However there are a couple more skills or skill nodes that are affected by healing effectiveness:
Transplant has a node, that is considered healing (Siphon, which makes the Pools Of Blood heal the player)
Voaltile Zombies Necromantic Fervor is considered healing
Bone Curse has a node (Bone Feast), that heals the player each time Marrow Thief (on kill chance to grant Bone Armour) is triggered.
There is one more thing that I have never tested myself, since I usually play with necrotic skills instead of physical ones, but Soul Feast has a node behind the physical conversion, that makes Soul Feast’s Soul Fragments “grant health” instead of ward. The tooltip is not clear if this is considered healing or if its “health gained”.
To answer your question how useful healing effectiveness is for Lich: It depends on your build.
The strongest interactions are definitely Rip Blood and AoD’s Absence of Life.
Rip Blood is not particularly strong offensively, but makes a great secondary skill if you can trigger it with Bone Curse and/or Transplant for Example.
AoD’s Absence of Life is ridonkulous when you use it with Reaper Form, basically negating Reaper Forms decay for the most part, leading to almost infinite duration of Reaper Form, if you don’t get nuked out of Reaper Form.