Alright, let's try this again.
Hypothetically, if... (ALL OF THE FOLLOWING HAPPENED)
1. Brutalizer's flat armor penetration did not stack with Black Cleaver or Ghostblade...
2. Black Cleaver's percent armor penetration were slightly nerfed...
3. And Brutalizer and BC's flat armor penetration are nerfed from 15 to 10...
Would it be OK to keep Black Cleaver on Dominion? Opinions, now!
1. Stacking BCs will still give me ample AD, CDR, flat pen, AND HP. It doesn't seem this is changed, unless all the brutalizer and derivative flat pen becomes unique, rather than just brutalizer not stacking with the others.
2. You're actually nerfing early game power of champions quite a bit.
3. You make it harder to actually make arpen worthwhile, it's becoming worse than season 1, for most champs, and the ability to stack penetration and remain squishy is something that should be open to assassins (I mean, where would Leblanc be if that weren't an option?).
So, it seems to me the issue of BC itself isn't really addressed that much, but the issue of stacking penetration as a squishy assassin had been taken too far.