I honestly think Kyurem-B is right on the edge of broken. While it's obviously held back by its speed and Ice typing, you can't ignore its stupidly high base stats. Base 170 Atk is absolutely insane, giving its Outrage jaw-dropping power. Heck, specially defensive Jirachi is 2HKOd almost all the time by CB Outrage with Stealth Rock down. Even the standard Ferrothorn in 3HKOd, so unless the opponent uses Leech Seed + Protect, Ferrothorn actually has a shot of being killed by CB Outrage. That Atk stat is so high that Kyurem-B can run full defensive investment and still be more powerful than a Jolly Salamence. This is obviously complimented by Kyurem-B's great base 120 SpA stat, giving it far the best overall offensive status in OU and making the mixed sets all the more dangerous. You've also got insane bulk on Kyurem-B that even some defensive Pokemon would love to have, even bulkier on both sides than a Ferrothorn with equal EV investment. No common OU Pokemon has the overall bulk of Kyurem-B, with only a handful of lower tier Pokemon that can match or beat it, and there's no Pokemon in OU or lower that can match it at all for power. That combination of raw power and excellent bulk is one thing that I really think has pushed Kyurem-B over the edge for a while now.
However, one big problem I have with Kyurem-B is that I still see no reason as to why it was necessary to drop it in the first place. It's not like it was a Pokemon that was formerly OU and had no reason to continue being banned. I know there were arguments that Kyurem-B would be a good new Genesect check and could help balance Rain and Sun, but Genesect ended up being voted broken and banned, and Rain/Sun have been brought up several times as potentially broken aspects of the game even after Kyurem-B was dropped. If Kyurem-B was dropped down for that, then it just seems like another case of dropping potentially broken things just to keep other potentially broken things in check. I also think it's apparent that dropping it didn't help since, again, Genesect was banned, and Tornadus-T (one of the best Rain abusers out there) was banned, with Keldeo (another dangerous Rain abuser) being suspected in the near future. What we pretty much did was drop a Pokemon that was already insanely powerful in its own right and put even more pressure on stall, which was already hindered by powerful Pokemon already present in OU.
All in all, I'd consider Kyurem-B to be broken. I also see no reason why it was unbanned in the first place, and it's just one more burden on stall in OU. Get rid of it.
However, one big problem I have with Kyurem-B is that I still see no reason as to why it was necessary to drop it in the first place. It's not like it was a Pokemon that was formerly OU and had no reason to continue being banned. I know there were arguments that Kyurem-B would be a good new Genesect check and could help balance Rain and Sun, but Genesect ended up being voted broken and banned, and Rain/Sun have been brought up several times as potentially broken aspects of the game even after Kyurem-B was dropped. If Kyurem-B was dropped down for that, then it just seems like another case of dropping potentially broken things just to keep other potentially broken things in check. I also think it's apparent that dropping it didn't help since, again, Genesect was banned, and Tornadus-T (one of the best Rain abusers out there) was banned, with Keldeo (another dangerous Rain abuser) being suspected in the near future. What we pretty much did was drop a Pokemon that was already insanely powerful in its own right and put even more pressure on stall, which was already hindered by powerful Pokemon already present in OU.
All in all, I'd consider Kyurem-B to be broken. I also see no reason why it was unbanned in the first place, and it's just one more burden on stall in OU. Get rid of it.