In describing their days of being "inseparable troublemakers," Bryon distills their roles in the hustles they would perpetrate. The distinction in their partnership is that Bryon's role was not as criminally significant as Mark's. Bryon would be "the hustler," the one that would rope in the target, while Mark carried out the criminal activity. The contrast brings out where they both are in terms of the propensity to do wrong and the ability to be brought back from it. Bryon's acts were not as criminally driven as Mark's.
The contrast helps to show that there is a difference between both of them, even though they are close to one another. Bryon does not demonstrate the moral lapse and transgression that Mark does. Mark lacks the understanding of "right and wrong," as evidenced in his descent into criminal activity through drug dealing. Bryon might have been the hustler in their relationship, but it was a temporary role that reflects where maturity and understanding lie within him. The contrast highlights this condition and Mark's lack of a moral compass in terms of criminal activity.