User blog comment:Deshiba/Circumventing armor for marksmen/@comment-24795478-20150520121219/@comment-4022742-20150520165114

Except that Last Whisper is Armor penetration and The Black Cleaver is Armor reduction. Which is in no way the same thing and are not interchangeable concepts, circumvention encompasses both. - Sincerely a Dutchman

I never suggested getting it when you have someone else in your team that already got it. Usually by the time you get to your penetration item, you will be able to see if one of your allies already has it and judge the situation from there.

Apparently I glossed over the champion specificness of the passive. Thank you for the heads up.