Just from a few battles, I can easily say that Kyurem-B is not broken. I have a team centered around Choice Band Kyurem-B that is doing more work without it than it is with it (Timid Specs Gothitelle to trap Adamant Brelooms, and Jolly Mamoswine/Scarfmence to beat the other Brelooms). In fact, Kyurem-B has proven to be more of a hindrance if anything. Of course, there are situations where it is helpful (Doesn't care as much about Scarf Genesect as other Dragons do unless Gene runs moves like Flash Cannon or Iron Head). It also has that impressive bulk and not giving a shit about Mamoswine helping it out. Hell, my Jolly Breloom's Mach Punch did around 66% to an opposing Kyurem-B.
What seems to bring Kyurem-B down for me is its low Speed and weaknesses to common types. It's slower than every OU Dragon-type except Dragonite, so you can revenge kill it with Salamence/Garchomp/Haxorus/Hydreigon as long as Kyu-B isn't Scarfed (most of the ones I run into are not, and basically all Kyurem-B on the ladder are Adamant). Not to mention that it gets pretty much no noteworthy Physical attacks except Outrage, Dragon Claw, and Fusion Bolt (please, Freeze Shock is a joke), so it's also predictable to the max (and walled to death by Ferrothorn!) I can see it being a solid OU Pokemon since it doesn't really care about Mamoswine (unlike other Dragons), but due to all of its flaws in the OU metagame, I think it should definitely be unbanned.
"If you put the federal government in charge of the Sahara Desert, in 5 years there'd be a shortage of sand." - Milton Friedman