The Necromancer is Underpowered Reason 9: Physical and elemental damage sources

All classes can achieve both physical and elemental damage, and most have some reliable way to deal elemental damage of at least two types. This is useful because elemental immunities are common in Hell, although perhaps not as common as poison immunity. One skill that makes all of this especially easy is the paladin's Vengeance, which deals all three types of elemental damage at the same time. But not every approach needs to be so compact. One of my characters is a tri-elemental sorceress that uses Frozen Orb, Hydra, and Charged Bolt. If a monster is immune to two of those, the third spell will kill it. Dealing multiple types of damage is vital, and the necromancer is the worst class to pull it off. As I've already argued, poison necromancers and bone necromancers have too few skill points left over to achieve two primary damage sources. But for classes other than necromancers, magic or poison specialists are niche characters, not virtually the only options. Most characters rely on physical and/or elemental damage.

With the exception of hitting monsters with a weapon, and remember that the necromancer has no native skills that synergize with weapons except for Poison Dagger, the necromancer's only sources of physical and elemental damage are pets. Well, Corpse Explosion has fire and physical damage, but let's not get too crazy (it requires corpses as ammunition and is not suitable as a primary killing mechanism). I'm not going to reiterate my problems with pets. Already wrote that post. But I don't even have to. Even ignoring the limitations of skeletons, they simply don't match up to what a character of another class can do with a suitable weapon. Elite equipment does help summoners, but really, since skeletons don't get much better from the necromancer's own equipment, it's all about the +skills. Other characters may be more reliant on equipment, but in the end, they have more damage output, more sustainability, more versatility, require less time to set up, and are just outright better. That's true for the skeleton warriors and their physical damage and it's also true for the skeletal mages and their elemental damage.

Curses have their own limitations, and I've written about those as well. However, curses aren't really the problem. The ones that I noted as being useful (Amplify Damage, Decrepify, Lifetap, and Lower Resist) are actually quite good. It isn't the curses that really stifle the necromancer, it's the lack of anything to go with them. Barbarians get Frenzy, Assassins get Dragon Talon, Amazon's get Strafe, Paladin's get Zeal, and Druids get Fury, just as examples. If the necromancer got even a single skill that could deliver weapon-based physical damage so quickly and with such force, Amplify Damage and Decrepify would look amazing. This is why the runeword and unique items that give a chance to cast a curse on striking are so good. If the necromancer had some skill that could actually give him damage output, he'd be powerful. No need to rely on items giving a chance to cast curses when you can just cast them yourself. Simlarly, if the necromancer had some skill or skills to generate respectable elemental damage, Lower Resist would look amazing. Sure, Lower Resist is good for poison necromancers or for sorceresses if playing with friends, but the necromancer doesn't have a way to take advantage of his ability to make monsters vulnerable to elemental damage on his own. Skeletal Mages just aren't enough.

This might seem similar to an earlier reason in which I deplored the necromancer's inability to use weapon-based damage, but it goes deeper than that. Sorceresses have similar problems, with Enchant as their only real melee skill, but they can easily attain massive elemental damage to make up for it. Other casters, such as druids can also achieve respectable elemental damage. In fact, every class has the capacity to, with either physical or elemental damage, hit harder than the necromancer can. He is stuck with magic damage (which takes all of his skill points and is substantially weaker than what a barbarian or paladin can do with magic damage) or poison damage (the most common immunity, with no viable way to get another major damage type).