No, Sherlock is not Rodney. There are a lot of differences, but they're both very extreme men with their intelligence and their feelings about everyone else's lack in that department. They both get that in the Johns someone who will say 'hey, that's enough. Time to go cool your jets'. Both the Johns are intelligent in their own ways. They're a bit tightlipped and let just enough slip to stay interesting.
I don't think being a gentle, easygoing and nice person automatically screams sub. There are people out there that would crumble under a harsh master. I know I'm not into any kind of pain, and humilation would just make me depressed.