Just played a game where a Riven was able to get: Black Cleaver, Last Whisper and a brutalizer. This isn't particular gold-intensive or hard to acquire build, but it allowed her to tear through any member of our team with impunity,

I, as Singed, just melted in front of her even with 200+ armor and 4k HP.

The math, I assume went something like this:

Armor Penetration:
8% from Masteries
-6 from Masteries
~-10 from Runes (?)
-25 from Brutal+Cleaver
-35% from Last Whisper
-30% from Black Cleaver stacks

Meaning a total of -41 from Runes/Masteries/Items after ~58.14% (multiplicative stacking of 8%*35%*30%) Pen/Reduce from Runes/Masteries/Items.

Meaning my 200 armor turned into 75, possibly less if my math is off or she had more than normal in Runes.

That's a total reduction of 125 armor or more, which allowed her, on multiple occasions to burst me from 100-0 in just a few swings (I counted one instance I think she dropped me in 4 swings + ult).

I understand giving character a chance to mitigate tankiness or 'counter' some level of armor items...but this is insane. I had a very good early game, a solid mid game and got DEMOLISHED late game because, as a tanky character, I had literally no way to counter the amount of damage and armor pen that character could buy.

For for less gold than I'd already spent getting my HP and resists, she was able to mitigate everything I'd bought.

TL;DR: New penetrator/AD items are OP as hell. QQ

Players

Please address your lack of patience and willingness to search for information. There is already a change on the PBE that is most likely going to be implemented next patch. Until then, bear with it.

The only change I saw on PBE was Black cleaver not stacking - this was with only 1 cleaver...

As Singed did you not build the triumvirate (Randuin's Frozen Gauntlet)? What about the RoA - wasn't that your first item? Together that should've given you ~300+ armor and ~3500 hp (roughly, with ult). Shred goes first, takes your AR down to 210, then apply %pen: 210 x 0.92 x 0.65 = 125.6 - 47 = ~80 which would mean you went from taking 25% damage to blocking 40% damage. So apparently Riven with just 220 AD managed to do 5000 damage; I think that's what Riot needs to balance. Of course I still have to ask: why didn't Riven cough up poison 'til she pushed up daisies?

Sounds like all that Riot needs to fix is the non-unique flat armor pen, maybe. Afterall, if Riven starts stacking Cleavers & Whispers, 2 RoAs, 1 AA, 1 Mask, and a DC should counter that quite well.