Still under a month and only just saw this, kinda interesting to think about.
tbh that is a good point. Effectively there could be a Pokemon that is so overpowered that it can beat everything in every other tier including ubers. It seems impossible but if that were true I'd assume it would just not be allowed to be used, and in which case there would be no point in Game Freak making it because it beats everything else singlehandedly, ruining the "fun" of Pokemon. Perhaps said Pokemon would get an item that specifically would prevent it from being overpowered or an ability or something (in which case it'd be a complicated ban if it were to be used), but... I'd still say that's kinda impossible, I don't really think Pokemon is designed for one thing that could beat every other Pokemon in the space of four moves. So yeah I really don't think there will be anything that's too strong for ubers, because Arceus is meant to be the most powerful and even it can be beaten. :x