Slight Kassadin buff

Now before you down vote me to oblivion and post how you think kassadin is tooo stronk, just hear me out....

Right now, every time you level up Kassadin's ultimate, the effective cooldown goes up. By effective cooldown, i mean the the time it takes for the stacks on his ultimate to disappear. Right now, the cd of the teleports goes from 6 to 4.5 to 3 secs on cd. However, the time it effectively takes for the stacks to wear off is 14 to 15.5 to 17 secs. I personally find it ridiculous that an ultimate basically goes up in cd as you level it up, especially one that doubles in mana cost every time you cast it.

My proposed buff is that the time it takes stacks to wear off also goes down each time you level his ultimate. so instead of 20 flat seconds, it scales 20 to 15 to 10 secs. I feel that it would keep early game roaming power down where it is, yet help his late game if actually does build like an assassin, and not like ryze.