That about says it. Seriously, is there a reason why someone would want a Kassadin on their team? About all he can do is kill steal. If you see a Kassadin with a lot of kills, it's only because he happens to be very good at kill stealing, but not at getting them to that point.
PERSPECTIVE TIME! Lets compare the champion, Kassadin, in his entirety, to, say, Ashe's ultimate, nothing else, just her ultimate.
Kassadin scenario: An enemy is low on HP, and is escaping. Out goes Kassadin, warping closer, closer, slow, silence, a bit of mana drain, kill.
Ashe ultimate scenario. An enemy is low on HP, and is escaping. Out goes the ultimate, flying fast, closer, hits and kills.
Yes, Ashe's arrow has to hit, but Kassadin also has to survive, it's a gamble whether he'll catch up without getting ganked or not, not to mention he can't go into the base with his low HP and squishyness.
In conclusion, as is, Kassadin as a whole champion, all his abilities included, is about as useful as one single ability.
Why do I bring this up? I like Kassadin, and occasionally try to play him with a group of friends, but really the only reason to play him is because I like him. If you're in a 5 man premade, against a 5 man premade, nobody would want him in a strategically put together team because the entire champion of four abilities can be replaced by a single ability. As for his silence, yeah, useful, but your average stun not only keeps the target from using abilities, but also from moving. Lasts about as long too.
Yes, there is a bit of exaggerating, but does anyone else see my point?