6 bans is more like an inconvenient phase of the rank process because of how many champions there are. Why not do away with bans all together? Increasing the amount of bans is preferable, but let's face it, probably not going to happen.
There are times when a couple champions are genuinely overpowered or broken, typically due to bugs.
For everything else, there's counterplay.
Because there are always those set of champions that nobody wants to play against.
Especially at lower elos, a lot of people don't know how to deal with certain champs (kat) and end up losing the game from champ select.
