I think John and Rodney are both control freaks, but it manifests in completely different ways because one of them's an introvert, and the other an extrovert. Extrovert Rodney wants to control the world around him; introvert Sheppard wants to be in complete control of himself. He can roll with the punches so long as he's secure in himself. He may be socially maladjusted, but I think he's actually pretty much at peace with himself, which gives him all the grounding he needs.

(I really shouldn't discuss Sheppard characterisation. It's way too close to my heart, and the fandom hardly ever agrees with me. *sighs*)