Kassadin's Concept
I see one glaring flaw in Kassadin's design: The fact he's specifically anti-magic.
Here is my biggest reason for the need to make him less anti-magic, and simply more of an assassin who uses it:
Not all of the Void creatures are Magic oriented. If he's supposed to be fighting them, why is he only suited to tussle with half of them?
(Don't even start on "Kog's a Mage" No. He's mainly a markman and played that way.)
Are all AD heavy.
Vs.
Being AP.
It's time to either change his lore or change his passives to make him able to fight ALL of the monsters he's trying to rid the world of. It made sense when it was just Cho'gath and Malzahar, but now it clashes too hard.