[typon77]

I've tried a Sub Mixed Cube set like that, and Fusion Bolt is superior in most of the situations I encountered. The main problem with running a Dragon STAB is that Outrage locks you in, which is something that a Substitute attacker like Kyurem doesn't want, as it can force you to switch out with a sub intact, wasting the offensive pressure and wall breaking spree that Kyurem could've been on. On the other hand, an unboosted Dragon Claw just doesn't hit hard enough on neutral targets (i.e. the main things you would use it on). Meanwhile, Fusion Bolt gives you an excellent super effective coverage move, which is definitely a a great boon on a powerful mixed attacker. The two special moves (Ice Beam and Earth Power) get great neutral coverage, so I've always found the extra neutral coverage move to be unnecessary.