As a former Kyurem-B Player, I'll add my two cents.
Kyurem-b has a horrible movepool. It can really only run mixed sets. It has amazing base stats, but a horrid typing. With Breloom running around, and Scizor (Less seen now), it dies fairly easily. It can't set up, and is destroyed by entry hazards. If you want to use it in a team, you need to build the team around it. Haxorus is much better, since it has all it needs to survive. Haxorus also has similar Attack, less special or bulk, but a little better speed and can set up.
Most of the time, Haxorus is more favorable over Kyurem-B. The better typing, movepool, the fact that it's not killed by hazards or priority allow it to be usually more favorable.
Here is a list of some things Haxorus wants that Kyurem-B has.
The ability to take out steels.
Now, Kyurem-B would love some of Haxorus' toys.
Reliable STAB (Kyurem-B would kill for Ice Punch)
My opinion? Kyurem-b becomes BL. Normal Kyurem is better than him. Higher special attack blizz spam. So, yeah. There's my stuff.
As Blue Harvest said it already gets some good STAB, plus Haxorus is only 2 base speed points higher than Kyurem; it's nice to beat other base 95s, but still isn't too significant.