All stories have some kind of meta-text. Sometimes, the story is a rigid allegory where the author's intent is dictated by the underlying subject matter. Sometimes, the lack of connection with anything is the meta-text.
There are also literary camps, like those who adhere to "death of the author," that intend to completely divorce the author's intent.
I tend to lean towards a blend of the two: a) What did the author intend? and b) What did the audience receive?
Lately, media production seems to lean towards the iconoclastic. You thought you knew your heroes? Well, now your heroes are an empty shell of their former selves, replaced with even more empty shells. Where your heroes used to have a narrative arc, instead, they start out perfect.
There's a place for perfect characters, if you understand the genre. For example, Mary Poppins is "practically perfect in every way." But the narrative arc isn't really about Mary Poppins, as such.
Having said that, I assert that Mary Poppins is not a Mary Sue.
First of all, what is a Mary Sue, anyway?
The term "Mary Sue" comes from the name of a character created by Paula Smith in 1973 for her parody story "A Trekkie's Tale" published in her fanzine Menagerie #2. The story starred Lieutenant Mary Sue ("the youngest Lieutenant in the fleet — only fifteen and a half years old"), and satirized unrealistic characters in Star Trek fan fiction.
Source: Wikipedia
I see the Mary Sue archetype having the following traits:
In my opinion, Mary Poppins falls short of this definition because she has experience that informs her expertise. Mary Poppins' intent is to be upstaged. I would assert that Mary Poppins doesn't even bend the rules of the setting because she's not the only one who can alter reality (i.e. do magic), in the story. She just happens to be better at it.
There is this notion that in order to make room for new, "better balanced" heroes, the old heroes must be torn down and trashed. Can you imagine reading a sequel to Tom Sawyer where the new hero must stamp out the old Tom Sawyer in order to replace him?
But often, that's what we have. And it's a result of extending and prolonging IP (Intellectual Property) beyond the author's original intent.
In a nutshell, headcanon is the accepted and received story, apart from the original author or additional authors of a particular IP, that survives the official canon of that IP. It is the natural result of "death of the author," when the author goes off the rails.
A great example of this is "Han Shot First." The headcanon of many fans was that Han shot first, so when Lucas fiddled with it, many fans just didn't accept this.
Here are many of the changes so far:
My headcanon is that Han Shot First, it doesn't matter what you change or if you add "Maclunkey." But at least Lucas wasn't trying to tear down Han Solo. If anything, Lucas' intent was the opposite, and that's at least admirable.
All this to say, if the new media has gone off the rails, it's best to just let them do that. If you don't like it, just don't watch it. This includes avoiding ... alternative methods of getting media. Don't even let them blame pirated downloads for undercutting their revenue. If the new stuff is bad, just rewatch your old DVDs. You're not missing anything.
. . . and by the way, in my headcanon, Luke only drinks blue milk.
