It really could use a buff. A non-boss enemy that gets hit by it should be dead, especially if they don't have a shield, but yellow enemies usually take multiple shots to kill. There's no reason for that.
Arc Blade could use a PvE buff, too. It's way too much risk to bother with as it is.
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In pve arc blade is pretty weak. I mostly just use it as another means to go invisible.
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That's exactly what I did before Gunslinger had the option of invisibility. Most Nightfalls had Lightswitch, so Arc Blade was almost entirely a no-go there, and almost every step of VoG had suicide bombing enemies. CE and PoE both have enemies higher leveled than you who will wreck you in melee range and likely won't die in one hit, so it's not much help there. Basically it's invisibility on demand and that's it.