I'd really like to just point out one more thing (and thanks for your nice response on the council, blara, I actually agree with you now!)
A lot of people have been complaining about overcentralization, but I think they need to rethink some things. People use Pokemon like Mienfoo, Misdreavus, and Murkrow because they are good. Philosophically speaking, there should, at any given time, be 6 best Pokemon in the meta. Granted, they may not synergize super well, and those 6 may sometimes change, but there should be an objective way to define this based on number of available sets, % of the meta said Pokemon can beat, and ability to work with other common Pokemon. We haven't found a way to objectively identify these 6 Pokemon ever, in any metagame, nor is it likely that we ever will.
A competitive metagame is one in which people are using the best Pokemon in the meta. What you need to understand is that people using inferior choices for style points are not playing competitively. People trying out new things as a potential counter to something commonly used are metagaming, but not if their potential counter is objectively inferior to another Pokemon in the meta. A "competitive" Pokemon needs some sort of niche: and that niche may allow it to rise into prominency or be too insignificant to matter in the long run.
Again, and this is mostly philosophical: there is a clear cut distinction between a competitive metagame and a diverse metagame. They are not always mutually exclusive, but whether or not they are mutually exclusive IS NOT UP TO US, IT'S AN INHERENT ASPECT OF GAME FREAK'S CREATION OF THE POKEMON IN A GIVEN TIER THAT WE HAVE ESTABLISHED.
I believe LC is currently a competitive tier. It is overcentralized, but I believe taking more attempts to decentralize it at this point in the metagame to add diversity are wrong. The reason is that the commonly used Pokemon (people often point to Mienfoo, Misdreavus, and Murkrow - likely 3 of our hypothetical 6) are good, but not imbalanced. Usage does not justify any degree of overpowered-ness. Only stats, movepool, typing, and other components can do that. A Pokemon's effectiveness in a metagame should not be qualifications for being banned. This leads to people not learning to adapt to a meta, ever. Competitively speaking, the best Pokemon that are not inherently overpowered (and most people seem to agree Mienfoo, Missy, and Murkrow are not) should be used as much as possible in order to create the most competitive atmosphere possible.
Eventually, you might counter, people would be fighting the same teams of 6 v 6 Pokemon. The great thing about Pokemon is that even in those circumstances, move choices, who they lead with, EVs, and moves on individual turns would still differ. However, a metagame in which everyone is using the same 6 mons would never last as people would learn to adapt to that exceedingly predictable. In turn, a new 6 Pokemon would rise (perhaps including some of the previous "elite 6") allowing a just as competitive metagame.
If you're worried about diversity, I don't think competitive Pokemon is necessarily for you. What you want is a bunch of different choices where all Pokemon are created equal and games would mostly if not entirely be won merely in teambuilding. To call that healthy for a competitive environment is, in a word, foolish.
Edit (In response to Corkscrew; why were Misdreavus, Murkrow, and Gligar unbanned): These Pokemon were unbanned due to the belief that they were not actually broken, merely banned rashly (Murkrow is a good example of this; as I think it was banned before it had Brave Bird, and if i recall correctly, Gligar only actually got discussed for a few days after people bandwagoned on AcroBat, hyped it endlessly, then banned it). In the end, Gligar was banned (although not due solely to that AcroBat set as its first ban, mind you) again. In the meta previous to this one, Mienfoo was arguably more dominant than now (except in the period Gligar was there) and the metagame was just as stale, revolving heavily around Mienfoo (44% in November 2011), Gastly (who has since been replaced by Missy, at 35% in November 2011) and Chinchou and Scraggy (28 and 24%, respectively, in November 2011). And in December, the last month we had "real" stats before the unbannings, Mienfoo went as high as 51% and Gastly all the way up to 40%. All of this is much worse than anything our current stats portray by as much as 20%.