We have elaborated (sort of) that the physical defense is not as useful as the special defence, albeit it is higher. That's because of its weakness for Fighting and Stone moves, both which comes as physical moves usually. It doesn't help you to tank Earthquakes when they follow up with Stone Edges. Besides, even 252/+252 Kyu-B cannot prevent a 2HKO by Breloom's and Scizor's CB priorities; Ferrothorn still kills you with two Gyro Balls and Iron Barbs. Surviving Terrakion's Close Combat once is a perk, but not the goal of a defensive Pokemon. I rather recommend to play its stengths, its resistance to Water and Electrics and its neutrality to Ice.
Kyurem-B @ Leftovers
EVs: 232 HP / 252 SDef / 24 Spe
- Fusion Bolt
- Ice Beam
- Hidden Power Fire / Dragon Tail / Roost
Thats a logical advancement of the Substitute set. I can't bring Kyurem to fight against rain without backup with subs because of its vulnerability to Scald. With enough SDef your substitute survives Scarf-Toeds Hydro Pump in rain, LO-Starmie's Ice Beam and specially defensive Heatran's Lava Plume outside of rain. These are only the most extreme cases, stray Scalds in rain won't be able to break through you anymore.
If you ask me, I will say that Dragon type moves are redundant with Electrics/Ice. Unless we want Mamoswine dead that badly we should joss Dragon Claw.
For some reason I can't really get warm with CB (no pun intended). Most of the time it feels like playing an one-trick pony; without the ability to switch moves you offer yourself as setup fodder for either steel types after Outrage or Landoruses after Fusion Bolt. Also, Ferrothorn is still in the top ten of the usage list, who can tank both moves and retaliate with Gyro Ball. Maybe I am doing it wrong.