Nah. Arceus is fast enough to get a CM in if your opponent has to switch in an answer to it. One Calm Mind Boost gets him 471 SpD and 443 HP, which is huge.
252 Naive Life Orb Mewtwo Aura Sphere vs. 248/40 Calm Arceus +1 : 33% - 39.3%
252 Timid Choice Scarf Kyogre Water Spout vs. 248/40 Calm Arceus +1 : 40.2% - 47.6% (in Rain, after SR)
252 Timid Choice Specs Dialga Fire Blast vs. 248/40 Calm Arceus +1 : 49.2% - 58.2%
252 Timid Choice Scarf Reshiram Fire Blast vs. 248/40 Calm Arceus +1 : 49.2% - 58.7%
252 Timid Choice Scarf Shandera Overheat vs. 248/40 Calm Arceus +1 : 54.6% - 65%
252 Timid Choice Scarf Shandera -2 Overheat vs. 248/40 Calm Arceus +1 : 27.5% - 33% (ie. Shandera Overheat doesn't 2HKO)
252 Timid Choice Scarf Heatran Flamethrower vs. 248/40 Calm Arceus +1 : 35.2% - 42% (no Flash Fire)
252 Timid Choice Scarf Heatran Earth Power vs. 248/40 Calm Arceus +1 : 22.6% - 26.6%
252 Timid Life Orb Darkrai Focus Blast vs. 248/40 Calm Arceus +1 : 39.7% - 47%
252 Timid Leftovers Ulgamoth +1 Flame Dance vs. 248/40 Calm Arceus +1 : 46% - 54.2%
All of these pokemon have 130 SpA or higher and all of these moves do neutral or super effective damage.
252 Naive Life Orb Mewtwo Aura Sphere vs. 248/40 Calm Arceus +1 : 33% - 39.3%
252 Timid Choice Scarf Kyogre Water Spout vs. 248/40 Calm Arceus +1 : 40.2% - 47.6% (in Rain, after SR)
252 Timid Choice Specs Dialga Fire Blast vs. 248/40 Calm Arceus +1 : 49.2% - 58.2%
252 Timid Choice Scarf Reshiram Fire Blast vs. 248/40 Calm Arceus +1 : 49.2% - 58.7%
252 Timid Choice Scarf Shandera Overheat vs. 248/40 Calm Arceus +1 : 54.6% - 65%
252 Timid Choice Scarf Shandera -2 Overheat vs. 248/40 Calm Arceus +1 : 27.5% - 33% (ie. Shandera Overheat doesn't 2HKO)
252 Timid Choice Scarf Heatran Flamethrower vs. 248/40 Calm Arceus +1 : 35.2% - 42% (no Flash Fire)
252 Timid Choice Scarf Heatran Earth Power vs. 248/40 Calm Arceus +1 : 22.6% - 26.6%
252 Timid Life Orb Darkrai Focus Blast vs. 248/40 Calm Arceus +1 : 39.7% - 47%
252 Timid Leftovers Ulgamoth +1 Flame Dance vs. 248/40 Calm Arceus +1 : 46% - 54.2%
All of these pokemon have 130 SpA or higher and all of these moves do neutral or super effective damage.