I think it depends on what the relationship is...partner, apprentice/side kick, and hero support aren't really synonymous. They describe different relationships. Hero Support strikes me as more of an oracle or similar role, partner is equal partnership obviously, and I don't think apprentice or sidekick is offensive, I mean maybe hero A has a decade of experience and is teaching hero B. Doesn't mean B will always be A's sidekick, but come on, if you're in that situation and you demand to be an equal partner, well it's just a bit silly, you're learning.
Of course, this all depends on what the heroes in question are interested in defining a relationship as.