Again, no, they really don’t.
When people think of a necromancer, they think of a cloth-wearing caster who raises the dead. That is quite literally how they are represented, not just in multiple forms of fantasy media, but also in World of Warcraft, where there are many, many notable necromancers, including Kel’thuzad, Heigan the Unclean, Dar’khan Drathir, Darkmaster Gandling, Gothik the Harvester, Noth the Plaguebringer and so many others.
Whenever anyone has asked for necromancers to be a playable class, that is what they’ve asked for. This was the case before Wrath of the Lich King, and it’s been the case since then as well. A cloth-wearing caster that uses death magic and raises the dead.
People who want to play a necromancer do not want to play a death knight. Which is something they’ve explicitly stated in every single thread asking for a necromancer class since Wrath. They don’t want the necromancer to be a 4th spec for warlocks either, because warlocks do not use death magic. They use fel and shadow magic and are known as the demon summoning class.
There is plenty of room for a necromancer class to exist without infringing on the class fantasy of the death knight, the spec fantasy of unholy, or the mechanical nature of demonology warlocks. In fact, many of the core abilities that necromancers in World of Warcraft use are not used by any class; that goes for abilities that the necromancer unit in Warcraft 3 had as well. It’s just a matter of picking up the pieces and putting them together in a way that is unique and provides the experience that necromancer players are looking for.
Personally I would give them a tank spec, a DPS spec and a healing spec.
The tank spec focuses on summoning a skeletal or flesh golem (replacing all other summons) and using abilities to empower its attacks, taunt enemies and defend itself from enemy attacks. It would create the first retail cloth-wearing tank class.
The DPS spec would focus on summoning and empowering a single undead minion that can be changed based on what is needed at the time, be it single-target melee DPS or ranged DPS, or AoE melee or ranged DPS, as well as a singular skeletal knight for tanking purposes that would only be good enough to tank open-world enemies like hunter pets or the warlock’s void walker.
And the healing spec can revolve around fleshcrafting and bone-mending. Twisting muscles, bone and sinew together to mend wounds directly but also giving you the option to cast spells that would redirect damage taken by allies to you, allowing you to then use life-stealing death magic to keep yourself alive.
There you go, three unique specs that don’t infringe on any other class’s identities while allowing necromancers to flourish as a class all on their own.