So what you want is a banlist in between the banlist and OU? That's a little excessive, no? You don't take the best of a tier in any sport and separate them into their own tier. Then take the ones below that an separate that into its own tier. Pokemon's the same way. Just gotta deal with the top tier stuff, and keep the metagame fluid through thought. Bans, in the long term, lead to the watering down of a tier.