Cursed blade is insanely OP and should be gutted/remove like today.
Straight up this item isn't remotely closed to balanced. It complete ruins the game. It hard counters everything and the only thing that hardcounters it is assassins deleting the CB user before they can auto a couple of times.
It's statistic insane in terms of DPS but since the DPS is hidden via not doing actual damage and just reducing HP it's been getting a pass. At the same time it's also arguable the best defensive item as the best way to reduce damage against many comps is simply to deny them from being 2/3 stars and reducing their stars reduces the damage against your whole team unlike PD/DT/Thornmail ect. Ironically it's also one of the better utility items because the level reduction also counter draintanking and chops defensive abilities like Braum's and Shen's to pieces.
I would care. But just use fodder at the front and put your mages in the back or use assassins as you have stated yourself. Geez. Get good.