Vayne Q cooldown to low

Vayne Q cooldown with zero cdr is 6/5/4/3/2 and 2 seconds is way to low of a cooldown when she goes invisible for 1 second, so basically Q is a one second cooldown on Q when you are playing vayne correct. Then you add on top that Vayne Q is a auto attack reset that does up to 50% bonus dmg. I understand that Vayne has a weak laning phase, but her late game dmg is so insane that its basically impossible to put a vayne behind where she is useless. Over all Vayne Q should be atleast 2.5 second cooldown at max rank and she would be some what balanced