yeah, they have a balance policy that basically says, "fuck under powered items and skills. if it sucks, just use a better one. no one is being hurt by underpowered skills" so lots of stuff stays shit. arc, chain, elemental hit, cleave, sunder, glacial slam, etc.
rare do they get small buffs. (sunder was)
on top of that, what you have is, overpowered gear. Thats where things really stand out. few skills are really broken op. gear however. Shavs, taste of hate/vinktars/dying sun, ,etc. You could kill shaper with elemental hit, or autoattack, with the right set of gear.
There is occasionally skills that suck balls normally, but right just the right setup. great. Arc stands out like this.
Arc as a skill sucks balls these days. it fell behind with powercreep. ball lighting just utterly shits on it. Self cast or totem. Its not worth ever using Arc. However, arc does have a means to not just be viable, but excel. Mines/traps. Arc is uniquely powerful in cluster trap/mine form. If you use an AOE spell in cluster mine/trap, you will notice they pop aoe, and usually 3/5 of the aoe will hit any given target. If you use a projectile, they will fire off towards the target or pack, and same deal, any given target even with pierce will only get hit 1-3 times out of the 5. Nova's from lit trap, same deal. 8 projectiles per trap.. but still they spread out and do not overlap 100%. Arc autotargets. 5/5 will hit on target EVERY time.
arc 70% damage. 2-7 chain.
remote mine. 49% more mine damage.
minefield 21% less. +2 mines.
+2 mines passives.
so, arc with 500 damage average hit single target.
will be about 700 damage average hit with remote mine.
And, 560x5 for 2800 damage average hit with minefield+2 mine passives.
Just those, not even including mine/trap damage vs spell damage scaling. nor chain x7, potentially chaining back to primary target.
GGG certainly did not plan or intend Arc to be only viable via traps/mines.