My version:
Unit ------ Dark Knight ------ Death Knight ------ Champion of Darkness ---
Ability ---- Curse Strike ----- Curse Strike ----- Curse Strike
Ability ----------------------------- Zombie Strike ----- Dispel spell
Unit ---------- Undead ---------- Death Herald ---------- Banshee ------
Ability ------- Aura of Terror ---------- Aura of Terror ---------------- Aura of Terror ---
Ability -------------------------- Devastating Grasp -------- Shrieking Wail
Ability ------------------------------ Unholy Word or Strike of Sorrow -----
Take a look – one knight has two attacks with different debuffs, while the other has a free cast.
The distinction between the Death Knights is lost. In my opinion, comparing casts and abilities is not the best solution.