I think about some of the great duos in fiction. Tarzan and Jane, Sherlock and Watson, Batman and Robin, Clark and Lois, Kirk and Spock, Xena and Gabrielle. Every superhero needs a counterpart...either to make them look good, or be their confidant, someone to rescue or merely someone to love when they aren't busy fighting for The Greater Good. And occassionally they screw the Greater Good for their partner. Sometimes the needs of the many don't necessarily outweigh the needs of the few...or the one. Sometimes you've got to save the one. (Just ask Jesus about the one lamb vs the ninety and nine.)
Spock was baffled by this, or at least he pretended to be. I myself think he eventually got it. At the end of Star Trek 4, when everyone was facing court martial, did he not say stoicly, "I stand with my friends."?
And some pairs take turns being the hero, y'know? Jane couldn't fight off Clayton but she DID get to rescue Tarzan...giving him a home, a place where he belonged. Gabrielle saved Xena's butt more than once and without Watson providing some stability, (that's a good friend that lets you live with them, play your violin at strange hours and smoke opium.) Sherlock wouldn't have been able to use his devastatingly cutting intellect. I think Sherlock was also an egoist and Watson knew it, constantly praising him.
I note that my list of characters...all of them are superheroes in one sense of another. I mean, Kirk WAS the only man to ever beat the Kobiyashi Maru...even if he DID have to cheat. (And in my line of work, cheating is not a bad word. ) Heck, Xena killed gods. Okay, by that season the writing had totally gone to hell, but the fact is, from her first episode she could do stuff nobody else could. Heck, her battle cry alone practically qualifies her.
I think we like these characters because they represent mankind just a step or two beyond what ordinary men can do...and we like them because they love someone who is ordinary. All of the sidekicks are pretty alpha too in their own right...but Robin will never surpass the Batman. Someone pointed out his surname of "Greyson" wasn't an accident. The son of...the shadow of the grey one. He follows in the footsteps but Dick will always be in The Batman's shadow.
Gabrielle inherited Xena's mantle in the horrifying last 2 or 3 minutes of what would have been a stellar finale. She never wanted it, I still argue that it doesn't fit..but even if she lived out the rest of her life traveling around seeing who could "use a girl with a chakram," she would never surpass Xena. She would make sure of that anyway, being the chief scribe for Xena's exploits. There will never be a show called "Gabrielle: Pacifist Sidekick," y'know?
Something else...I think the sidekicks are mentally stronger than the heroes. Superman needs Lois more than she needs him. Sure, she would be sad if he died (and he did and she was,) but when Lois died, Clark cut himself off from the rest of the world. Kirk risked an entire ship, an entire crew's record in order to go save Spock...and it was all on a hunch. Spock wouldn't do anything like that unless confronted with some irrefutable logic, probably provided by Bones. Gabrielle died and Xena went crazy. Xena died...more than once and while grief stricken, Gabrielle continued to live and make plans for herself. Now who is the sidekick?
So is there really no hero/sidekick at all? The world perceieves it as such but to the duo involved, how do they perceieve themselves? Lois Lane would NEVER describe herself as a sidekick, Spock would deem it illogical to call himself a "sidekick" to Kirk and while Gabrielle might self deprecatingly call herself Xena's sidekick, an entire Amazon nation would take umbridge at that particular notion.
So what about us non fictional mortals? Those of us who live lives not found in the funny papers or between frames in the television or the movies? Is it better to be the hero or the sidekick or nothing at all? I've been a sidekick, I've been a hero and sometimes both in the same relationship and now I think I am a mere mortal. Sometimes I miss my theme music.