Hi so I’m new here and to competitive Pokémon and I had a couple of questions so if someone could answer them it would be greatly appreciated ^_^
So first I was wondering how hoopa unbound was in OU since he has a 680 base stats like other Uber tier legendaries? And the same with kyurem b?
While Hoopa-U is certainly not a bad option, there's better options overall for a wallbreaker for teams (mainly Tapu Lele). 160/170 attacks are amazingly strong, but a measly 80 speed leaves it vulnerable to common things you could find in offensive teams (Landorus-T, Tornadus-T, Kartana, Garchomp, Greninja, all of them have access to either U-turn or just very strong attacks), not to mention is horribly 60 base Defense and Quadrupedal weakness to Bug (U-turn is a common move on offensive oriented teams, which is a Bug Type).
It also is outclassed by other common pokémon in either one side of the spectrum:
- Physical wallbreaker: Mega Mawile (amazingly high Attack thanks to Huge Power and one of the best typing [Steel/Fairy]), Mega Medicham (similar case, sky high Attack due to Pure Power, but this time with a pretty good 100 base speed and access to Fake Out), and other things with >120 base attack (many of them have either better speed, a way to boost their speed, better typings, etc.).
- Special wallbreaker: Tapu Lele (insane power in Psychic moves thanks to terrain, actually has speed, and Fairy is overall better than Dark), Mega Alakazam (Trace is a cool ability to check many mons that have immunity based abilities, Intimidate, Speed-boosting, etc.), Magearna (Better typing, have a Speed-boosting move) and other things I will not mention to not make an needlessly long post.
On Kyurem-B, while is certainly intimidating, have enough counterplay to not overcentralising the meta compared to Uber-tier mons. Bulky Steel Types are able to switch into it's Ice Type attacks, there's many faster threats that are able to revenge kill it, and the fact that lacks an spammable physical Ice move prevents to transforming it into a fearsome physical wallbreaker, and force to become a decent mixed wallbreaker (The closest things it has to a real STAB are Ice Beam, Fusion Bolt and Subzero Slammer from Freeze Shock).