Some dumb things I noticed about Last Whisper

tl;dr: Why is it a good item on Assassins?

So I'm sure most of us are at least somewhat familiar with the metabalancing triangle for damage:

• Tankiness shuts down Burst. Building into Effective HP will typically scale faster than one can build into Burst Damage. Along with this, because there's a very strict hard limit to how much damage a champion can do in a single ability rotation, this will mean that having the effective damage to survive a Burst Champion's rotation will typically lead to a direct advantage in a fight.
• Burst shuts down DPS. Because DPS directly scales on time, a Burst combo, if executed fast enough, can completely nullify a DPS Champion's chance to fight back. Typically, a dedicated DPS champ will not have the Effective HP to survive a Burst Champion's rotation, leading to the typical situation of Assassins and Burst Mages shutting down a caught ADC.
• DPS shuts down Tankiness. As mentioned before, what separates Burst from DPS is that DPS scales directly on time. Unlike Burst Champions, a DPS therefore has no hard limit to their damage potential, assuming they stay alive for that long. With that given, even despite a Tank's possibly massive Effective Health, this makes DPS the way to really hurt Tankiness; with enough time, a DPS' damage will simply out scale Tankiness. [These are generalizations, not strict rules]

With this in mind, I'd like to preface this post by saying I have absolutely no problem with ADCs building Last Whispers and killing tanks. While you can argue they do it too well, and if you provide objective evidence it would be a good argument, we must accept that it is a given that the DPS class of the game is literally doing their job as they are supposed to be doing if they are killing Tankier champions.

But...what about AD Assassins?

See, the disturbing thing about the Last Whisper is that it is extremely gold efficient against targets that don't build any armor. I can provide specific examples for specific champions if someone wants to ask, but it's generally a given that the Last Whisper is not an item to not have by your 4th dedicated item slot at most if you're a Physical Damage based champion, regardless of how squishy the enemy team is. What happens now is you have Burst Champions, a damage type that's supposed to suffer against Tankiness, picking up one of the most easily identifiable dedicated anti-tank items in the game in their attempt to kill some of the squishiest champions in the game. Odd, right?

What's especially dumb is that, depending on the context of the situation, this means there's not really much of a way to counter AD Assassins at all in the way of itemization. The typical response to a Burst Champion getting fed should be to buy the resistances to them; Tankiness to counter Burst. With the Last Whisper however, bought resistances are literally cut down by 35% (and a bit more, when you also consider base Armor). What happens as a result of this is there's less interesting Counter Building interaction in the game (Carries are willing to sacrifice their damage potential to buy Armor to survive an AD Assassin's burst? Why even bother, they're gonna buy LW anyway) and some of the world's oddest match ups (You know there's a problem when the Assassins start 1v1ing Bruisers and have the potential to win consistently).

I'm not going to pretend I have a one size fit all bandaid solution to this issue, but I just wanted to point it out. While I'd say the concept behind the Last Whisper is perfectly balanced within the context of AD Carries, AD Assassins being able to utilize this item extraordinarily well is just the oddest thing to see. It challenges any concept of unique health vs damage interaction in the game, it sets a really weird precedent for this game being an anti armor item that's efficient against targets who don't build armor, and it probably contributes to a whole lot towards negatively affecting interesting gameplay with letting AD Burst challenge Tankiness.