Why Gangplank will be broken in patch 6.1

So. As an avid PBE follower, I found that Gangplank's barrels will now have 60% BONUS Armor penetration, from 40% TOTAL armor penetration. Now, if you look at the changes to last whisper, you will find that you get 45% BONUS armor penetration. This means that Gankplank's Barrels will shred through 105% of all armor that tanks build, but do slightly less damage to squishies. But then again, if you run Critplank.....( ), you crit on 90% of your barrels, dealing 250% damage to everybody who is in them, and negating all of their bonus armor.