Should uber Pokes be banned in Leagues?

[Azureth]

For example, was it right to let someone use a Latios and a Darkrai in a league tournament? Seems as if there would be a rule against that.

 

[Kenshin5]

https://www.pokecommunity.com/threads/270122
This is essentially already discussed here but is more generalized. So please post in this thread instead.