If Assassins are meant to be feast or famine. Why not add some risk to dusk-blade users?

Currently, there's no downside to picking up Duskblade, it's a sweeper that drastically boosts offensive power. It's probably the most popular item in League at the moment.
If Assasins are meant to be high risk, feast and famine champions - Why is there almost no risk in just buying this item and going all in at any point of the game?
Why not give the item another subtext like "After procing Nightstalker, take 15% extra damage from enemy champions". That way it becomes a high risk-reward like Mejai's, rather than just take this item every game with little to no counterplay.

would apply itself over the bleed, potentially making you take MORE damage than you should.
no mana regen / mana regen yet a must have if you're a mage against a mid assassin
auto attacks consume mana
reduced crit damage as long as you have low crit chance
reduces your damage while activated
- unless you can stack its waste of gold and slots.
- long time investements.
Sword of occult - removed
Leviathan - removed
Questionably so -
- if you aint around your buddy its only gives 1700g worth of stats. With actual cost of 2300g. Also you kinda taking true dmg at the rate some squishy target would do. So its kinda downside as well.
or