Agreed, it's not a situation where it's like Moody, which is broken even on Glaile. If it's only broken on one pokemon, that pokemon should go.Just giving my two cents here, but banning Libero would imply that its also broken on raboot or every mon who has it (which of course its not). The solution there would be a complex ban on Cinderace alone to ban Libero on Cinderace but it's doubtful that the Council will do that.
Having said that, while I think Cinderace is broken, at least there's some counterplay to it. Nothing restricts team building quite like Urshifu, you need to essentially dedicate 2 team slots to make sure you don't auto lose to it.