For another example:
As much as some Inheritance Cycle fans dislike Roran's parts of the story - even going so far as to skip them - he actually presents a good counterbalance to Eragon's major role as a Badass Normal. And while Nasuada has fewer chapters than him dedicated to her point of view, she is no less an important character than the other two. Both have feats that hold a candle to Eragon and Saphira's deeds, and they are both important not only as supporting characters, but protagonists in their own right. There are some that say that Roran is the true hero of The Inheritance Cycle, and I quite frankly agree. Sure, Eragon killed Galbatorix, albeit indirectly, with the help of the free Eldunarí, but the Empire would still have won the larger battle outside were it not for Roran Stronghammer's bravery in defeating Lord Barst - with a spear, no less! And Nasuada is perhaps the only one to have withstood Galbatorix's physical and mental torture without breaking, though she nearly did were it not for Murtagh.

As is famously said in movie business: "There are no small parts, only small actors." (Okay, that latter bit may have just been from The LEGO Movie's "making of" documentary bonus feature, but it's no less true.) Everyone has a role to play that is no less important than the heroes' deeds. How would the Hobbits have defeated the tower, were it not for Treebeard and his fellow Ents? Who would have gotten Sam Flynn to visit the old arcade were it not for Al? What would have motivated Batman to bring justice for Gotham City were it not for him witnessing his parents' murder? Who would have told Spiderman that great power comes with great responsibility but his dying uncle? Every great hero needs not only a great villain, but great support and motivation - and more often than not, those latter two come from people who otherwise play a smaller role in the grand scheme.

These are just my thoughts, but you're welcome to add to them.