its been clearly stated
Passive: Kassadin draws energy from spells cast in his vicinity, gaining a charge whenever a nearby champion, including himself, uses an ability, capping at 6. Upon reaching 6 charges, Kassadin gains the ability to cast Force Pulse.
ok if this ability can be casted after amount of spells are casted why the FAK does it have 6 seconds cooldown?
Vi's Excessive Force has 1 second cooldown and stores charges every X seconds and can be casted 2 times but Kassadino needs X amount of spells to be caster before he is able to use his ability and also he has to wait 6 more seconds to cast it
If i drink a glass of water and then fill it up why would i have to wait 6 god damn seconds before i am able to drink it again?