To be fair, his E should keep the charge system but allow him to use it even with zero charges but have it's power cut into 1/6th of its max power.
Basically each charge increases its usefulness until he reaches 5 charges like normal it does its original live values. Example 0 charges 1/6th of efficiency, 1 charge = 2/6ths, 2 charges 3/6ths, 3 charges 4/6ths, 4 charges 5/6ths, 5 charges 6/6ths (One whole equal to live values).
This way it'll give the player some decision making in deciding when he should use it, throw a weak one out for low damage and slow or wait until its fully charged for the max dmg and slow effects.
It was placed there in the first place because he was called the anti-mage. But that is a farcry to what he is able to do now, since a real anti-mage is now categorized better as playing an early game assassin. I could see Kassadin as a fighter, but really he is just all over the place with low base stats and base damages on his abilities and the late game aspect is just a sad place to wait to bring him into light cause it really isn't all that fun going through that risk of giving up that early game in favor of it.
One of the main reasons I've stopped maining Kassadin plus all the constant changes he has gone through, he really doesn't have a defined place even in his niche.
In terms of the other original anti-mage that you don't see as often is Galio, and Galio is really more of an anti-magic bruiser in respect to how things have evolved.
EDIT: In more ways then one, he just feels like a bstrd child version of Fizz that has to wait to build items late into the game or a crappy assassin with hardly any real burst.