Blade of the Ruined King isn't even bought on the only champions who used to buy it.
Vayne, Kalista, Yi, Warwick, Shyvana, and more don't even consider this item anymore. Even against an HP tank like Mundo it's not even worth considering. It's absurdly expensive, provides no noteable powerspike, and doesn't scale with other items. It's active is very weak compared to other items such as ghostblade which in addition to having strong actives are still gold efficient. It's one of the least efficient offensive items in the entire game, coming in at a disgusting 73% gold efficiency without the passive. Even in extreme circumstances, the passive is not going to be doing enough damage to make up for the horrible stats.
Most importantly, the champions who used to build this item are not as dominant as they were in this item's prime, before the nerf. It needs a reworked effect, new effect, price drop, or buff to the stats or passive. When a cookie cutter offensive item with no real niche is never purchased, it's obvious there's a huge issue with it's power or cost. It's not like a banshee's veil or Wit's end that is strong but rarely bought due to nice effects. It's an item nearly every AD champion in the game would consider buying if it wasn't so horribly overpriced. It's clear that the stats are the issue. We've gone more than an entire season without any champion even touching this item.
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and the second as a tool to counteract HP stacking with the powerful on-hit effect. For instance, the first could be named Blade of the Ruined King (with the flavor text: A gift of the King to his duel champion), whereas the second could be called Freljordian Whaling Harpoon (flavor text: Made for killing Leviathans).
has become the generic item against high health targets.
or
. Just ask 
gives life steal and heals you... it scales with resistances as those makes each point of health gained by life steal more valuable
.