This item is a necessary evil. Yes its overtuned, but it needs to be. Changing AD assasins and AP assasins so they can be easily outplayed by adcs and have delayed burst was a large part of ADCs becoming so dominant. Their predators aren't as much of a problem. (That paired with a lot of things). Duskblade is way too important for assasins to do their job. The assassin rework necessitated this item and this item NEEDS to be strong. I don't frequently play AD assasins so I'm not biased, I find it annoying to deal with also, but if this item is gutted it makes ADCs lives EVEN easier.
The only thing that needs changing about this item is that it should deal less damage on ranged. In my opinion ranged champions shouldn't have access to this items proc at all but that's another argument.
This needs to be the formula
Burst > DPS > Tank > Burst
and at the moment we are miles away from that. We don't need to go any further.
TL;DR - Item is toxic and overtuned but needs to stay that way so assasins can do their job and adcs aren't even stronger.