The Necromancer is Underpowered Reason 7: His most powerful damage source is a clumsy gimmick

Corpse Explosion does work well for clearing massive hoards of weaker monsters (although, as I've already stipulated, not as well as the hype surrounding the skill would indicate). These situations are a large portion of the game, but they aren't all of it. For me, at least, boss fights are the heart and soul of Diablo II. Against strong enemies, every character puts away those crowd-clearing skills and brings out the big guns. And the bigger the better. Rapid attacking is key here, whether it's nuking bosses with a spell, firing a bow as though it were a machine gun, or swinging away with a melee weapon. Increased attack speed, faster cast rate, life leech, mana leech, deadly strike, open wounds, and crushing blow are all valuable here. Some of the things that are good here are good everywhere in the game, but often, strong monsters call for a bit more. Precautions, like extensive pre-buffing or changing gear, that might be overkill elsewhere, tedious, or just unnecessary can make perfect sense if the monsters are strong enough.

If you haven't played necromancers, particularly summoners, in Hell, you can be forgiven for not seeing what's coming next. But if you have experience with summoners at high levels and you don't see what's coming next, shame on you. The necromancer's skeletons, although they can achieve respectable damage, can't be improved much by preparations in the way that other characters can do with their damage sources. Summoners do have a way to get massive damage, though: Revives. Besides being improved by Skeleton Mastery, Revives also take on the abilities of the monsters that the skill was use on. The necromancer can turn this into a boss-killer by going to the River of Flame in Act IV and using Revive to grab a bunch of "urdars." These guys have crushing blow and a large group of them will make quick work of a single target like Diablo or Baal. In addition to their massive damage output, they are very difficult to kill.

Out of all the pets available to any character, Revives are potentially the toughest tanks and the hardest hitters. Unfortunately, they are clumsy to use. I want to make it clear that I do not say this based on my unwillingness to use a build that requires skill or my desire to play mindless left-click-and-win characters. The problem with the Revive skill isn't that it requires finesse. It's just needlessly awkward. Revives behave stupidly and require constant babysitting to get them to beat up on enemies. Even though they can deal insane amounts of damage, it takes telestomping, which requires a specific runeword armor, to get them to actually focus on an enemy. They also tend to wander off and if they get separated from the necromancer, they disappear, so Teleport is virtually a requirement just to keep them from vanishing after thirty seconds. Revive cannot be used on certain corpses, such as those of unique monsters, which makes some sense (even I don't want necromancers to be able to run up to Baal with Colenzo, Aachmel, Bartuc, Ventar, and Lister as pets). But the worst limitation is the timer. Revives only last three minutes, no matter what you do. With proper planning, that probably is enough time to kill any single enemy in the game, but it requires rushing against a clock in a way that no other character has to do. I'm all for games requiring some skill, but trying to telestomp bosses with Revived urdars before the timers on the Revives run out just isn't fun.

Revive is the ultimate display of wasting potential. This skill potentially provides the most numerous and the most powerful summoned pets, but in practice, they just end up being the most annoying and ineffectual. Monsters that zero in on the necromancer with deadly accuracy mostly just wander around when they are Revives.