A word about champs that "aren't" overpowered...
... strictly due to the fact they can be counter-picked.
I'll just give near-perfect example of
. While she may not be the best when the meta fluctuates to Tank, as it does, she's still the perfect example of a champion who can be countered, but must.
In high ranks, she's no harder to play and deals no less damage. The only difference is that a good Katarina player will know when to pick her-- that is, when the enemy has little enough CC for there to be little to no counterplay against her, or when she'll have an ally who needs just as much focus to kill.
There are a few of these champions that "aren't" overpowered because they're susceptible to CC--like every other champion in the game besides Olaf. Refusing to change stats and scalings simply because the champion is vulnerable to the thing every champion is vulnerable to isn't balance when that's the only they they're weak to.
EDIT: Seems some people are confused about when Katarina is strong. It's okay, plenty of people don't understand that Akali doesn't have her ultimate before level 6, too. I pointed out that a GOOD player won't pick her when she's completely countered, but a half decent player won't feed even when she is, and will just roam and get kills after level 6.
If you're going to attempt to argue against my point, it doesn't help to say "but she can be counter picked" when that's the issue I'm addressing.