Just wanna point out that he did in fact tell you his necro build, zombie + provoke skeletal archers. I've personally seen the zombie hitting for 2.5k against a neutral resistance mob, so against lethargy puck, where crushing is effective, the zombie alone would be dealing something like 15k damage in that time period. Then with pound to slag you can easily hit for 10k on a crushing effective mob and with some other crushing hammer abilities plus the archers and precasted provoke, zombie and way of the hammer, and I could easily see it reaching nearly 40k damage. Especially if you start including damage buffs from potions etc.

Necromancy is actualy a really good skill, the reason nobody uses it is because you have to micromanage so much. You have to keep your pets in line, which also means you can't pull, you have to keep provoke undead and the zombie buffs going at all times during the fight and then the result you get is single target damage only which takes time to ramp up. In a normal group, because mob hp is so low, half the time your zombie will just be running between targets and standing around rather than actually attacking. Where necromancy really shines is actually elite soloing or very high hp mobs like the world bosses but in nearly all cases this is less than 1% of actual play.

Necromancy can also seem poor, especially the zombie until you get proper mods like the zombie speed buff. I did some testing and the zombie can solo a mob at around the same level as the ability without any mods in nearly all cases, but the problem is since it's so slow by default it's basically impossible to use until you mod his speed.