Cocky and rebellious John was a by-product of that erra. A bunch of white guys were trying to write about a black man but had very little knowledge of their culture or how they actually behaved except for a very generalised, almost stereotypical view of their life.
^I agree with your point, though I wish they would at least keep it as part of Stwearts character, like maybe he used to be more cocky dealing with anger issues from his time in the marines but mellowed out over the years.
One is a result of the other. John became a lot more grounded and diplomatic after Cosmic Odyssey where his arrogance resulted in the destruction of a planet. The guilt almost caused him to take his own life.