Westerns are actually a good example of the way Magical Girl stories feel to me at the moment. Westerns were so popular for so long that they basically covered all possible ground for stories and then began falling into the same traps over and over--every Western story was required to have shootouts or scenes of riding through the grasslands, and every small town had to look exactly like whatever you'd find in Blazing Saddles, to the point that the aesthetic itself risked becoming a cliche.
Westerns survived by adapting, though. You have your deconstructions like Unforgiven and The Revenant and so on, and then you have stories that adapt the Western style into new genres, such as the Star Wars series, or Cowboy Bebop, or a movie set in modern day like Hell or High Water. The classic idea of a Western from back in, say, 1950, barely exists now, but the genre still thrives with media like Hateful Eight, Yellowstone, _Logan, Red Dead Redemption_, and more. None of them play the tropes straight, though. I'm not sure there has been a single Western movie or TV show in years that sticks true to the old genre conventions.... Maybe the new Magnificent Seven remake? But I barely remember that one.
To me, the magical girl genre risks falling into the exact same traps, where the same aesthetics and story tropes become so codified that it stifles the genre as a whole. I personally feel very little interest in the magical girl stories releasing lately, so I may be biased, but it does feel to me like there is a declining level of interest overall in the genre too. I don't have any stats to back that up, though.
