I'm 54 now as a Boner Spear Necro and the play can be a little clunky on stuff like boss fights without a lot of adds or if you need a lot of movement (we don't have any). Otherwise it's fucking trucks. I was doing the world boss and helltide events and I 100% notice when I start spearing. The mobs health kind of move consistently with other classes like barbs/rogues but when I spear it fuck lops off huge 5% chunks. It's unreal. I don't even have all the right aspects/uniques yet. Normal dungeon bosses, and I shit you not, I could probably kill in 5-6 spear casts. Sometimes I'll cast three spears from full essence and it will take the boss down two pot pegs.
It's pretty cool, but I think it's not very safe until you get the god items and go the more defensive variant. I have no movement, no fortify, no pets, and limited healing outside blood orbs which I only have because I took an aspect that isn't even on my guide. I don't doubt though it's probably #1 or close for single target. Especially if you can shotgun them by boner bouncing off a corner into a big hitbox.