The thing is that BC has both percentile and flat arpen, it gives you HP, and CDR.
4 BCs = 40% CDR
200 AD, 1k HP, and a good amount of flat ArPen.

I am still not sold

Everybody is doing insanely high damage. New items made it so easy to do damage, its not even funny.
Tanks melting in 1 vs 1, squishy champs dieing in 2 shots.. most of the champs are now AD/AP carries..

So what now? Stack health and magic-resist and focus on defending against the lesser evil Black torch? Health has always been the only way to protect yourself against true damage (which is what armor penetration stacking has become), and with magic resist protects you against most health scaling magic damage.

Q. How do you feel about the current magic/armor penetration system?

They missed the big picture when looking at the overall balance in the armor penetration. If magic penetration can't stack "Eyes of pain limits 1 item per champion"; Why the heck should the armor penetration (brutalizer, ghost blade, and black cleaver) items stack with each other?

How could their item balancing team not pick this up if this patch is all about balancing armor and magic penetration?

^this would be a good start, making flat arpen passives unique, because that's what is taking people down to zero armor after all the % pen

I feel like it's broken.

TBH,I think that the item balance was perfectly alright before this blackfire and other stuff came out.I feel that all this was unnecessary,They should have simply added the new items (minus bft,that thing is extremely annoying to deal with) and gave the new arm pen formula.Cleaver didn't need any change.I used it on my Xin Zhao as a core item and it worked out excellently.

Now after these changes its nuke or be nuked so its unfun for me.I go nuke a person on xin with his e then his buddy nukes me,the cycle goes on and on till end of match with the winner being the team that won the first fight.

the problem with ad caster items and Support items is that the former are always bruisers wet dreams and the later are used as bruisers utility thanks (yeah i know bruiser complain and the l2p noob jabber) to the massive stats they get with their kits alone, so Cleaver or any other item made to boost ad casters will break bruisers and every support item made to boost support will break bruisers(hell innervating locket was removed because of UDYR although the wiki hides the fact and says Sona), there's a serious dramatical design error there, like old jax, where riot couldn't change anything before JAx's remake becasue every change would Buff Jax.

The game feels like a FPS death match now.