Yeh it will about double your boss damage, not counting its high base damage overall. You get free stormblast every swing.
This weapon becomes little suboptimal with really high end gear, because it is hard to max pierce for lightning and cold at same time (and you can't use stormlblast with axe to focus purely on lightning). It is sort of legacy feature of an item that bunch of axes have lightning procs (even innat axe proc, thunderfury, that every 2h barb axe has is lightning). It dates back when there was no skill restriction to swords and axes. Then it was introduced, axes got cold skills tree (skills that convert to cold both iceburst and gaze), but at the same time they still have their own lightning damage mods.