I think it's worth adding that UU was made to allow Pokemon that don't get used much to have a metagame of their own. It's not for weaker Pokemon (although it does so happen that it's generally weaker Pokemon that end up there).
There needs to be a cut-off to determine which Pokemon aren't used much.
Infact, if you read throught the old threads in PR, there's actually a few people that wanted less Pokemon (e.g. about 25 Pokemon) in Standard, so they actually wanted to raise the cut-off point, which would be giving us even stronger Pokemon in UU.
I still don't get why everybody panics every single time something goes to UU. If it's too strong, it'ss get banned, and it'll all be fine.