I guess my point is that Kirk refuses not because he's "Superman Kirk and Shatner has an ego" but because it's true to character. Kirk sees McCoy and Spock go through the "give me your pain" scheme, and simply decides he wants nothing to do with it. He wants to stay in his own reality. It's fairly consistent with his character, always rejecting the idea of paradise or taking the easy path. Heck, even in GEN he brushes off the highly addictive properties of the Nexus when he realizes it's just another con of sorts.But, that's not what Kirk says. He tells McCoy the purpose of his pain and unwillingness to just give it up. It's not just Sybok he's resisting.
I think Kirk's dialogue in that moment is spot-on...one of the defining moments for the character.