That would be the first two pokemon EVER in the tiering history to be put in UU with a BST 600.
Actually, Regigigas (may he rest in peace) gets the honor of having (over) 600 stats and getting banished to UU, actually, NU because of that horrid ability. Slaking is a heck of a lot better (single wise, both are pretty good doubles) than that.
But anyways. Kyurem...has a small movepool (gosh darn it, why did his special moves have to be two turn charges because otherwise, even resisted they'd hurt like hell and also, what up with that awesome attack and almost nothing to use it with?).
His advantages are his resistances to water, electric, grass, neutrality to ice...and his downsides are the weaknesses. Rock, Steel, Fighting are the only real ones to worry about (all dragons are weak to dragon except Dialga) because of that blasted priority although the good news is that Breloom will only revenge kill, not switch in with impunity like those dang steel types (Breloom sure don't want to be Draco Meteored/Blizzarded/Icebeamed etc to death). Although how common is Choice Jirachi out of curiousity? Because if that isn't so common anymore, you could x that off and Metagross is lesser seen. The real steel is Scizor which spells doom.
It's not really Steels (except Scizor) that are concerning, but the Stealth Rock and Choice Scarf Dragons and revenge Mach Punchers. If it wasn't for them, this would kick butt hard. Dragon/Ice is slightly overlapping, but it hits most types hard and getting spammed by Draco Meteors and Blizzards (in Hail which especially hurt) and Icebeams. Also, earlier a Dual Screen set was posted which seems interesting because if you keep Stealth Rock off, behind screens, Kyurem won't die to Mach Punch/Bullet Punch and will be able to kill/switch out of whatever comes in. I think Starmie would be a good team mate for the Kyurem dragon with Rapid Spin and being able to absorb those Punches as well as threatening back. You need to beware of the other moves at times (U-Turn/Bullet Seed) but when facing Kyurem, they're probably not going to do that (well maybe U-Turn spam because they expect Kyu to run maybe).
The movepool is disappointing yes, but it's somewhat useable. I doubt it would fall to BL but probably to that point like Milotic, Donphan, Cresselia where they were technically OU but are so rare you pretty much never saw them.
Focus Blast is a horrid accuracy move yes. But that has never stopped other Pokemon from using it, usually because they have nothing better or need the coverage. But it is staple on Gengar, Alakazam, Rankurusu, Darkrai, Voltlos, etc. Able to have it is far better than not so stop complaining about Kyurem's needing it to hit steels.
Is it good? Meh, maybe not in comparison to (should be banned to Uber) Latios but it isn't totally hopeless for Kyurem. Plus, it is cool looking (why do people think it's ugly?) and can do some stuff like Choice Scarf, Screen, Frozen World (not as useful OU but good Ubers), go somewhat mixed, etc. With Rapid Spin and Wish, it can be pretty deadly. They're are a lot worse Pokemon. The Kyurem hate is a little extreme and uncalled for, it's not perfect and there are a couple other things that do it slightly better (although Sazandora runs into the same Mach Punch problems) but it certainly isn't bad by any means and once Latios is most likely removed (Choice Specs Draco Meteor is ridiculous from Latios in particular) Kyurem will take it's place. But it will never fall to UU.
Actually behind Reflect (lol, everything is good behind a screen and how many still use Brick Break?) Wish support will make this thing beastly. Even Scizor and Guts boosted Roopushin will only deal enough damage that will be entirely neutralized by Wish. And Kyurem 2 hit koes back (Life Orb Modest Max special attack)...
Plus, think of a combo Dragonite+Kyurem the repeated but never specified Dragon combo (Dragonite appreciates the rapid spin and screen support). Dragonite pounds physically and takes the punches while Kyurem blasts special side. Kyurem does have a neutrality to Ice and it takes an insane Ice attack to drop Dragonite thanks to Multi-Scale while lets him survie pretty much anything.