As one of the few people who actively use Cobalion, I definitely think that it suits B-Tier better than C. Cobalion's excellent typing, physical bulk, and speed make it a very useful support and offensive tank, capable of taking hits from all of the tier's dragons and hitting back hard with an HP Ice. Its Taunt and typing really go well together at stopping stall, since pokemon like Ferrothorn or Skarmory can't really do much after they're Taunted, and can be eliminated with a few super effective moves. One of the best and absolutely most useful thing about Cobalion is the fact that it 'beats' Deoxys-Defense. Its Terrak-fast Taunt prevents even the fastest Deoxys from setting up nada, and Volt Switch allows you to quickly pivot to a set up sweeper to abuse Deoxys's weak seismic tosses or to scout a switch in that thinks they can handle Cobalion. Cobalion itself is a splendid lead- with a fast Taunt and the ability to set Stealth Rock, and then pivot to another member, possibly forming a Volt Turn core. It has decent offenses as well; 90 Atk and SpA certainly can do work to a weakened team, and with great coverage in VSwitch/CC/HP Ice, not much can take two hits. Cobalion's nature is sweet as well, x4 resisting Dark, Rock, and Bug, and x2 resisting Ghost, Dragon, Steel, Grass, Normal, as well as an immunity to poison. With these traits, it can function very effectively in today's metagame. It's Volt Switch, Taunt and Stealth Rock are perfect for Volt Turn cores, and it has great synergy with common pivots like Landorus-T or Rotom-W. Its typing lets it handle all weather starters well (with the exception of scarfed leads), since Tyranitar and Abomasnow, and Ninetales are disposed of through CC, and Politoed can be Volt Switched in the face. It's a great lure too, since many people send in their physical walls just to be Taunted it pivoted like Forretress or plain KO'd like Gliscor. The only drawbacks are it's slightly lower SpD, vulnerability to Genesect, Fire, and Ground type moves, and its lower power compared to a few other pokemon. With the right support, however, it can efficiently function as one of the most underestimated yet effective support pivots in the metagame.