“It’s not enough to bash in heads. You’ve got to bash in minds.” Joss/Zack/Jed Whedon
There are really a lot of reasons it was successful, but being able to tell a story is what enthralls people. It doesn’t have to be Marvel really, it has to be a good story.
What they are referring to is anyone can make a fight scene, or imitate someone else in real life. This isn’t hard. Weaving the fight into the story arc is the art.
Not every story has a happy ending. Sometimes, a character has to die. In life, some sacrifices for the better good must be made. That could include you as the sacrifice.
It is also about hard choices that divide allegiances. It is a no win and usually a blurred line as to where the divide between right and wrong exists.
Telling the story that involves emotions is always better than just stating facts.