sorry but im not a metagame bitch, i just play with whatever champ i like to use for the moment, so i only stick to what i can do....
i dont care for the lane i just choose one and try to do my best against the enemy i have, with the equipment i can afford in the match, i only go with rules when i know which type of champ in using...
Look, here's the thing: Kassadin is a strong champion. That's all there is to say about it. He IS, however, melee and an assassin. This is probably something that is not initially intuitive to a player. You just have to learn how to play with a melee character. They're tougher to play (at least for me), and I can understand why you'd find Kassadin weaker than he should be.
Zed/Ahri/Kassadin/Fizz have gotten a ton of attention lately because they can annihilate anybody by glancing at them. You know why that's a problem and Riot's nerfing it? Because it allows them to erase the ranged AD from the equation. Right now, everything is balanced around the ranged AD, how much damage they can do, and what you can do to stop that. The fact that armor is completely worthless right now is a direct consequence of S2 where tanks could build pure armor and ranged AD couldn't kill them for shit, so penetration was buffed and armor was nerfed.
Actually, penetration has always been strong. It has never not been strong. It has only become stronger than before due to the way penetration is calculated now (percentage before flat). Tanks were better because of this. They were not unkillable. They had approximately flat penetration * percentage penetration additional armor, which equals about 15 * .4 = 6 more armor, assuming 15 flat penetration and 40% penetration. And I'm just taking a very simple build. But, you don't gain much. The change made penetration just a little bit stronger.
What the change DID bring was AD assassins and casters into the game. This is because items that gave FLAT armor penetration were incredible. You can get like 40 flat armor penetration with just a brutalizer. Combined with the Black Cleaver (25% armor shred), and you see why AD suddenly rose heavily over the course of S3. It wasn't the ranged AD, though. It was Kha'Zix, Zed, Renekton, Jayce, Lee Sin, Tryndamere, Aatrox... Heck, even Riven and Shyvana are seeing decent play (Riven is awesome though, so there's that.) There wouldn't be as prominent or strong if there weren't such good flat penetration items.
Overall, the ranged AD gained very little power from the penetration changes.