Originally Posted by Fat Dark Fallen Angel
Kyurem is definitively not worse, because it has advantages over Kyurem-B. First, its higher Special Attack means that Kyurem's pure special attacker sets outclasses those of Kyurem-B. Second, Kyurem has Pressure, which is a valuable ability that combined with its bulk and great resistances to Water, Electric, and Grass, let it pull off an excellent SubRoost set
You're trading 10 points of SA for 10 points of defense and swapping Pressure for Teravolt. Not to mention the ability to go mixed, throwing uninvested physical hits like a max-atk Mence. Now, Pressure might be better for a staller(though uninvested DTail has it's appeal), but on a sweeper, Teravolt is well worth 10 points of SAtk.