No, the meaning has not changed over time. Have many people misused the term over time? Yes. That doesn't mean the meaning changed. "The Internet" is not an entity in itself. It is made up of people.
And who decided it? You? There have been countless discussions over the Internet about what the term "mary sue" and how it evolved. Google "Mary sue" and "Evolution", or something.
There is no consensus. It is not a language body. Just because people misuse a term does not mean the meaning changed, it means those people misusing it are using it wrongly.
But apparently, there is. You just said yourself that the term Mary Sue can only mean one thing. Either you are god, or someone made a poll and decided it can only mean one thing, completely ignoring the fact that it acquired a pretty much broader usage over the years. Was originally this usage wrong? Yes. But it has been used over and over and for so much time that it pretty much acquired an additional meaning.
There is a proper meaning for terms, please use them accordingly or people will tell you that you are wrong. That's what happens.
I shall from now on, only speak like a dictionary, ignoring the common sense and language evolution.
"I'm gay" "But you look sad".
"You are such an Hipster" "But i don't like Jazz"
Or the word Tsundere. Do you argue with everyone who uses that term "wrong" or have you simply accepted that the word evolved and its used in more broad ways?
Trying to defend this position is no different from being told to stop talking in class and going "but those other people at the back are talking too!" because it is not a defense. Two wrongs don't make a right. Three wrongs don't make a right. Ten wrongs don't make a right.
To be fair, the teacher could ask the whole class to shout up, and not only you. Fucking teacher. Maybe she hates you, i dunno.
Also, Two wrongs make a right. In Ancient Rome! See, things evolve through time!
Using the junior/mod defense to try and bail out of an argument you're losing in is bad form. It shows that you have no confidence in your own position in the first place, and you're trying to back away without looking like you lost. Unfortunately for you, we don't do that around here, so it's going to continue until you either have a decent argument, or you admit you were wrong.
#EnglishIsSeriousBusiness
I'm not trying to bail out. But i've been lurking her for a long time and i know about your past arguments. (You once banned a dude because he called some DS game graphic bad) So i'm sorry if i'm a tad afraid to answer your posts until i got past 300 messages.