70/70/75 bulk sounds mediocre on paper, but in practice it's not that bad since Camerupt is almost never hit super effectively. Fully invested, it takes all of the hits it needs to very well. Here are some calcs:
252 SpAtk Choice Specs Raikou Extrasensory vs 252 HP/252 SpDef Camerupt (+SpDef) : 30.23% - 35.76% (4 hits to KO)
This is the strongest move Raikou can throw at it, and it's still not even a 3 hit KO after leftovers and rocks.
252 +1 SpAtk Raikou Hidden Power Ice vs 252 HP/252 SpDef Camerupt (+SpDef) : 26.45% - 31.4% (4-5 hits to KO)
+1 HP ice hardly does anything.
252 SpAtk Choice Specs Rotom-H (+SpAtk) Overheat vs 252 HP/252 SpDef Camerupt (+SpDef) : 40.7% - 47.97% (3 hits to KO)
Easy switch in to any set as it'll do nothing after the special attack drop. Only thing to worry about is trick.
252 SpAtk Choice Specs Chandelure (+SpAtk) Fire Blast vs 252 HP/252 SpDef Camerupt (+SpDef) : 43.9% - 51.74% (3 hits to KO)
Barely not a 2 hit KO. This isn't a hit Camerupt wants to take, but it can if it has to. You're better off checking it than switching in directly.
Some other various calcs:
252 SpAtk Shaymin Earth Power vs 252 HP/252 SpDef Camerupt (+SpDef) : 30.81% - 36.63% (4 hits to KO)
252 SpAtk Shaymin Seed Flare vs 252 HP/252 SpDef Camerupt (+SpDef) : 41.28% - 48.84% (3 hits to KO)
252 Atk Victini V-create vs 252 HP/0 Def Camerupt: 47.67% - 56.1% (2-3 hits to KO) (can't switch in, but can check)
252 Atk Sheer Force Darmanitan (+Atk) Flare Blitz vs 252 HP/0 Def Camerupt: 57.56% - 67.73% (2 hits to KO) (same as above)
0 Atk Bronzong Earthquake vs 252 HP/0 Def Camerupt: 38.37% - 45.35% (3 hits to KO)
I'm using it with intimidate and leech seed support from Qwilfish and Shaymin on my team, so it often has an easier time switching in to resist as these calcs show. Really the only thing Camerupt shines at is checking Raikou flawlessly and not having to worry about random coverage moves. I realize it's not amazing and that it's worse than Swampert and Rhyperior, which is why I'm only nominating it for C rank as a niche replacement for two A rank pokemon.
252 SpAtk Choice Specs Raikou Extrasensory vs 252 HP/252 SpDef Camerupt (+SpDef) : 30.23% - 35.76% (4 hits to KO)
This is the strongest move Raikou can throw at it, and it's still not even a 3 hit KO after leftovers and rocks.
252 +1 SpAtk Raikou Hidden Power Ice vs 252 HP/252 SpDef Camerupt (+SpDef) : 26.45% - 31.4% (4-5 hits to KO)
+1 HP ice hardly does anything.
252 SpAtk Choice Specs Rotom-H (+SpAtk) Overheat vs 252 HP/252 SpDef Camerupt (+SpDef) : 40.7% - 47.97% (3 hits to KO)
Easy switch in to any set as it'll do nothing after the special attack drop. Only thing to worry about is trick.
252 SpAtk Choice Specs Chandelure (+SpAtk) Fire Blast vs 252 HP/252 SpDef Camerupt (+SpDef) : 43.9% - 51.74% (3 hits to KO)
Barely not a 2 hit KO. This isn't a hit Camerupt wants to take, but it can if it has to. You're better off checking it than switching in directly.
Some other various calcs:
252 SpAtk Shaymin Earth Power vs 252 HP/252 SpDef Camerupt (+SpDef) : 30.81% - 36.63% (4 hits to KO)
252 SpAtk Shaymin Seed Flare vs 252 HP/252 SpDef Camerupt (+SpDef) : 41.28% - 48.84% (3 hits to KO)
252 Atk Victini V-create vs 252 HP/0 Def Camerupt: 47.67% - 56.1% (2-3 hits to KO) (can't switch in, but can check)
252 Atk Sheer Force Darmanitan (+Atk) Flare Blitz vs 252 HP/0 Def Camerupt: 57.56% - 67.73% (2 hits to KO) (same as above)
0 Atk Bronzong Earthquake vs 252 HP/0 Def Camerupt: 38.37% - 45.35% (3 hits to KO)
I'm using it with intimidate and leech seed support from Qwilfish and Shaymin on my team, so it often has an easier time switching in to resist as these calcs show. Really the only thing Camerupt shines at is checking Raikou flawlessly and not having to worry about random coverage moves. I realize it's not amazing and that it's worse than Swampert and Rhyperior, which is why I'm only nominating it for C rank as a niche replacement for two A rank pokemon.