I think that high ban rates have made some champions better

Self fulfilling prophecy style. Like, Teemo. Teemo was an weird pick that almost no one knew how to abuse. Then baron laners started to ban Teemo out of trauma and people were like, damn, we should pick Teemo whenever he is available.

Same with Fizz. Fizz was an weird B-tier pick and most people would play him badly. Now he is perceived as powerful despite all nerfs, and people just pick him over and over again. Lots of decent Fizzes out there these days.

Now, Akali, Akali may be really busted. :P But lots of champions have been one tricked because of evident perceived power (ban rates) and are better in average than they were before people could ban.