So true, Chris. I forget who said this about the key to a good story, but it speaks to your point: “Simple plot. Complex characters.”
Re thinking about every character as if they are the protagonist, it just makes sense. Because in their mind, they ARE the story’s protagonist. When I interviewed Ava DuVernay, she told me about one script she wrote — I believe it was “Middle of Nowhere” — where she went through a rewriting process in which each draft, she focused on one character and wrote with them as the story’s focal point. Her approach isn’t quite like what I am suggesting, however the idea of writing a draft with one character in mind as the story’s ‘protagonist’ (even though in actuality they aren’t) is a great way to delve deeply into each of our characters.