And what if there was 2 variations, one being thornmail and the other building from warden's mail to reduce attack speed.
By the logic of LW items being balanced, items like this would be also be able to be balanced and "healthy" for the game.
Effectively bypassing a large part of a champs bought stats.
All of the arguments in favor of Last Whisper items would also apply to an item like this. Including things like it not being hidden power.