The problem is, that it doesn’t matter how it does in Ubers. The issue is how it does in OU. There are a bunch of Pokemon in Ubers currently that are actually really bad because of the pressence of Primal Groudon like Reshiram, Deoxys-N (which is outclassed by Deoxys-A) and various Arceus-Forme which are treated as seperate pokemon.
But if you let stuff like Reshiram into OU, it would wall the majority of the metagame or break through a bunch of pokemon thanks to its typing being better in that format compared to Ubers which is dominated by Ground and Flying Spam.
For more stuff like that I recomment reading this article about unviable Ubers:
http://www.smogon.com/articles/unviable-ubers
As for Hoopa being banned, I have yet to try him out. In theory, its offensive stats and movepool makes it really difficult to reliability stop it when running balance or stall which don’t use a lot of fast pokemon.
The specs set has gained a lot of popularity lately because it doesn’t need to waste evs on atk and go pseudo mixed with psyshock. It seems like a fair trade of to give up high base power physical move for lower base power more versitile special moves from its higher special attacking stat.