Focus Blast, the move that has a 49% chance of hitting twice in a row? Most of the Steels in UU aren't even hit Super Effective by Focus Blast and they wreck Kyurem. Registeel beats it with TWave and Iron Head, Escavalier gets a clean OHKO, and things like Suicune, Milotic and Chansey also exist which don't give a shit about any Kyurem set.
The most common Steels in UU are Registeel, Escavalier, Cobalion, and Empoleon (or rather, the ones that are viable) Out of those (and out of the Steels in UU) the only one not hit SE by Focus Blast is Escavalier. Every other Steel-type in UU is hit for SE damage.
Lets assume Kyurem is Hasty with 252 SpA EVs.
Unboosted Focus Blast vs:
Max HP Max SDef Careful Registeel: 39% - 46.2%
Max HP Max SDef Calm Empoleon: 50.5% - 59.7%
4 Hp Cobalion: 106.5% - 125.7%
Max HP Adamant Escavalier: 36.6% - 43.3%
LO Focus Blast (Mixed sets made to combat defensive teams) vs:
Max HP Max SDef Careful Registeel: 50.5% - 59.9% (2HKO after SR factoring Leftovers or switching into an Ice Beam or something)
Max HP Max SDef Calm Empoleon: 65.6% - 77.4% (Always a 2HKO)
4 Hp Cobalion: 138.1% - 162.8% (lol)
Max HP Adamant Escavalier: 47.7% - 56.1% (Considering Escavalier isn't weak to it...)
HP Fire obviously OHKOes Escavalier.
Every other Steel you might see (Aggron, uh Magneton?) is either OHKOed or... OHKOed... or is too crappy to bother with. And out of those Steel-types, Empoleon can't do jack diddly squat to Kyurem, Escavalier and Registeel aren't completely safe since Focus Blast still does a bucketload and they are both easy to wear down since they lack recovery and are slower, and Cobalion, while it can outspeed Kyurem, can't handle Focus Blast at all. You seem to be forgetting that Kyurem can do other things besides spam Blizzard. Its movepool may be crappy, but it has what it needs. Even if Focus Blast is inaccurate, it is still a viable, powerful move.
Bulky Waters are also out of the question. Milotic and Suicune really can't touch Kyurem...especially if it has a Life Orb or Choice Specs. They simply cannot handle repeated STAB Dragon-type attacks from something with the base Special Attack of Latios and the base Attack of Garchomp. Suicune can't even hit Kyurem with anything, whereas all Milotic manages is a weak Dragon Pulse that doesn't even 2HKO without investment.
You say that teams with any kind of defense block Kyurem:
Kyurem @ Life Orb
Trait: Pressure
EVs: 4 Atk / 252 SAtk / 252 Spd
Hasty Nature (+Spd, -Def)
- Draco Meteor
- Ice Beam
- Focus Blast
- Outrage
This set pretty much OHKOes or 2HKOes all of UU. Calm 4 HP 252 Def Chansey takes 47.7% - 56.1% from Outrage with Eviolite. Bold 4 HP 252 Def takes 43.6% - 51.6%, which are both 2HKOed after SR. Chansey needs 252 HP and 252 Def to avoid being 2HKOed by Outrage, but that opens it up to being worn down a lot more easily by repeated Special hits. Even Suicune takes a hefty 65.3% - 77.2% from Draco Meteor, easy KO range for a follow up Outrage or maybe even another DM. It also 2HKOes any Milotic set with DM + Outrage. Even 252 HP Calm Deoxys-D is 2HKOed by the same combination. Most of the other walls are weak to Ice-type attacks (Celebi, Nidoqueen, Zapdos, Donphan) or aren't fit to take Special hits (Dusclops, etc.). It requires a bit of prediction to use effectively, but it breaks up defensive cores like none other.
I find it hard to believe Kyurem sucks at breaking teams with "any kind of defense" when it has better Mixed capabilities then freaking Salamence. It has both base 130 Attack and SpA - why not use it?