I completely agree with this as a matter of history.
That said, the appropriation of a term in mass culture can often be different when other groups get ahold of it.
Well, then we should be more clear about the original:
"Mary Sue stories—the adventures of the youngest and smartest ever person to graduate from the academy and ever get a commission at such a tender age. Usually characterized by unprecedented skill in everything from art to zoology, including karate and arm-wrestling. This character can also be found burrowing her way into the good graces/heart/mind of one of the Big Three [Kirk, Spock, and McCoy], if not all three at once. She saves the day by her wit and ability, and, if we are lucky, has the good grace to die at the end, being grieved by the entire ship."
-Smith and Ferraro, who coined the term, in 1976
The original was a
parody, after all. It wasn't particularly positive in its connotation.
And, in later interviews, Smith has mentioned that James Bond and Superman can be considered "Marty Stu" characters (a term coined by the same women, btw), whose characterization is generally secondary to their being potent. Indeed, Kirk himself is kind of a Marty Stu, when you get down to it...
Later uses by others, then, aren't significantly different in
meaning. What's different is the intent and mode of use - today men will apply the term in a knee-jerk fashion to denigrate any capable female character, without the honest analysis to determine if she lacks appropriate characterization or flaws to escape being a member of the trope.
So, it is still a hammer - currently folks just hit things that aren't nails with it.