First off...You have to realize what it means to be a kage...Sasuke might be able to win against a kage but can not take on the kage mantel on his own...To be a kage means yes you might be the strongest shinobi in your village but you have responsibilties to take care of. To be a kage means to put the village concerns more important than your self and protect it by any means...and sasuke has problems putting anything more important than his own feelings let alone wanting to destroy the village he grew up in based off young ignorance and a temper tantrum.Like i said he might have strength to match a kage or even kill but will never be true kage level.