Blade of the Ruined King needs some changes to be a proper counter to health tanks.
Part of the issue is that too much of the power seems to be focused in the active. Call it good or bad the result is of the build path being from Bilgewater Cutlass in turn has made the item overall ideal for AD assassins, Jax, Trynda and Vayne. The idea I am suggesting is to make it more clearly defined as a tank killer instead of an assassin friendly item. This does however mean a different build path then it currently has.
Vampiric scepter (900) + Serrated Dirk (1100) + Recurve Bow (1000) + 400 = BotRK (3400) 40% attack speed 40 AD 15 armor pen Unique passive: deals 8% of targets current health as on hit physical damage (minimum damage from this passive is 2 + 1*champion level) (capped at 60 damage against minions and monsters) Heals for 10% of physical damage done by auto attacks or on hit abilities.
And yes this is because the current BotRK does not do a good enough job in being a reasonable counter to health stacking tanks. Hence part of the reason why Malphite, Mundo, Rammus and the like are sitting at a rather high win rate. With mages gettign nerfed in some ways such as higher MR being on items and no good options for reducing armor past masteries and LW an item that allows for a little more disregard of enemy armor would likely help.
Yes I am aware this might also be popular on assassisn as well given the 15 armor pen but with the lack of the active it isn't anywhere near as much of a problem on say rengar or Zed since you have to auto attack to get the % health damage. Both would likely be better off with Ghostblade in this case.
Just a idea but some things are a bit screwy after 5.22 when it comes to armor pen and reduction.