Simply put it doesn’t do enough ult damage against superarmoured bosses. It’s the only elf weapon that can’t kill a CW in one hit with the shade ultimate, against bosses it performs even worse.
If you crit headshot a rat ogre you will hit for 40.75 damage.
If you crit headshot Bodvarr you will hit for 31 damage.
However if you use the shade ult first you will hit the rat ogre for 203 damage, and Bodvarr for 31.5 damage.
In other words the shade ult gives you a 400% increase in damage vs rat ogres and a <1% increase vs Bodvarr, which is essentially nothing. Does that sound wrong to anyone else? The glaive heavy attacks also suffer from this to a slightly lesser degree, against Bodvarr you will deal just 18% more damage.
Admittedly all of the other elf weapons like dual daggers also have a very poor ult damage boost vs Bodvarr and Skarrik. However I think that the two specifically anti-armour weapons should receive a buff against those bosses. At the very least they should perform better than other weapons, instead of worse as is currently the case with the axe.