This cesspool has caused quite the ruckus in the balance department, causing him to be changed/reworked a variety of times into the current lackluster state that he is in right now (oh thank god...).
This guy was THE assassin-hyper carry that scaled tremendously well through the game. He did not just pick off one person, he picked off everyone while being virtually impossible to lock down, starting with your backline to everyone else. If Kassadin was on the other team, your team immediately began to argue because one - your first pick didn't ban Kassadin and let him through and two - he was disgusting to deal with. Who knew that a champion with a semi-spammable, longer ranged Flash that does damage, and a long ranged targeted silence that does huge burst damage could cause such trouble in a game where half of the roster has no mobility. Kassadin was globally banned in all forms of play. In competitive he was pick or ban across all regions - in solo queue, it was the same deal... minus the pick part since he was always banned (http://gyazo.com/5f3a85a990c33c15cbd0f9ebb4a03661 ).
It got to the point where they had to rearrange his kit so that he could actually see play without all hell breaking loose, it was unlike anything the game had seen before where a champion caused such a ruckus in EVERY form of play. He wasn't just a solo queue stomper, he was a stomper period. He will always be the main anti-mage champion who will make your life miserable if you're not careful. Sites such as Reddit started buzzing and the balance department took action - he is not as oppressive seeing as his silence has been removed (it only blocks projectiles now) and his ult is a bit difficult to outright spam since its mana cost stacks the more you use it within a time period, but it still stands that Kassadin's impact on the scene is one that will be remembered.
Ah, and that is just PRECISELY where you have gone wrong.
Let us resonate with the simple truth that Tim Burton is an excellent director, cinematographer, actor, and caterer. And please, it would just be an injustice to not put emphasis on "caterer." Good God, those snacks are MOUTH-WATERING. Any reasonable fop like myself should feel their salivary glands pumping right about now.
O' bless ye merry genitalman: Tim Burton, Enlightened Souls Advocate.