You just made me think of something. The shipping works (especially for
) because the characters stand well on their own, and instead of being defined by who they're with, when they have their own dynamic when together that may as well be its own character itself.
Take Super Boy and Mako. Superboy is a rightfully troubled as hell teen who manages to have an arc where he defines himself several times in the face of the person he loves and those who tempt him with the very powers he wants so badly.
What does Mako have? The most characterization he ever had involves a relationship. In fact, any characterization of the guy involves relationships - be it with Korra, Asami, or Bolin. Yeah, we had that little bit about the criminals he used to work for when doing his investigation for Book 2, but whatever came out of that. We never got any scene with Mako deciding it's best for him to be a cop. We never see him be given a paycheck and realize how different it is earning money as opposed to stealing to live, or how he and Bolin live in their own apartment when their family back in Ba Sing Se can only afford one place to live all cramped up.
In fact, why does Mako become a cop? Obviously for the convenience for the plot to have that investigation bit that ultimately reveals Varrick's treachery, but other than that, why?