I disagree that overcentralisation should be treated relatively. For one thing, there are questions whether anybody would want to play that game (in that "The definition of Uber" topic). There is also the question of whether the game will actually reach a point where banning any of the remaining pokemon will not increase the number of viable pokemon. There is also the concern that we cannot detect whether a pokemon should be unbanned. If the ban list contains every pokemon except for Pidgey, Magikarp, and Kakuna, then there is only one viable pokemon. If we ban Pidgey, there are now two viable pokemon. Obviously the right course of action should be to unban some pokemon instead, but how can we tell with a goal of making the game as decentralised as possible? It almost seems as if we would only stop when the ban list exceeds the number of legal pokemon.
Also, the idea of treating overcentralising relatively is equivalent to minimising the number of pokemon who are not viable. But why should we care how many pokemon are not viable? If GameFreak adds five hundred new shit pokemon I don't see why any effort should be made to accommodate them, even though the metagame could be be greatly decentralised by banning most of our current pokemon.
So instead I suggest constructing the uber list so that it contains as few pokemon as possible such that the number of viable pokemon is above some critical threshold. Then we would define "overcentralisation" as if the number of viable pokemon fell below this threshold, and we would say a pokemon is "overcentralising" if banning it would increase the number of viable pokemon above the threshold. Then it would be fair to say that if the metagame is not overcentralised then no pokemon can be overcentralising it.
It does not seem to me that there is a tradition of attempting to make the metagame as decentralised as possible either, which is why I did not address the notion above. I don't think we should be banning pokemon if we do not even agree on the purpose of making such a ban. Maybe there is no disagreement, but there have not been that many posts in "The definition of Uber" compared to this topic, even though here we essentially need the results of the other topic.