Can't disagree here.
They do that with everyone, from Bobby Da Costa to Hank McCoy to Justice and Firestar, yet not-one complains about this when they're on the Avengers and this wasn't a problem when she was a minor character for the X-fandom (but they probably didn't like her much anyway, for the sin of not being an X-man and a mutant) until M-Day and now suddenly this becomes a huge problem people care about. I'm curious whether the negative reaction to M-Day would have been had it been Bobby rather than Wanda. It's not like his stint on Avengers revolved completely around his mutant identity.
Wanda didn't make an impact on the Iron Man and Avengers United cartoons, not that they were Marvel strongest shows in that time period, but she had a fairly big presence in Wolverine and the X-men and Evolution. She may not have been a major character, but what they did give her was a huge boost in credibility outside the comics.
The MCU is not as restricted like the comics are, especially after the new tv branch got made which heavily incorporates elements from the movies rather than being reduced to mentioning in passing. It'd be one thing had her show been made in the prior tv incarnation but starting from the movies themselves already gave her a massive advantage in interest since she didn't begin on a Netflix production. Wanda being revealed to be Magneto's daughter in the MCU would be a massive twist and the movies are vastly more capable of intertwining the various sections of their brands than the comics are. Iron Man met Rocket Raccoon! Magneto himself would be a huge villain in the movies just because of who he is and people love the character, it's why he appears so much in the Fox movies. You're right, comics canon is malleable, that's why I think it's only a matter of time before it switches back.
Are you talking about the movies? She's been in the Avengers films since Age of Ultron and despite not being a major character her actions have impacted the plot - like in Civil War. The movie conflict starts over what she does on a mission. In Endgame her small role provides a huge victory over Thanos, something the Big Three Avengers can't do in half the time. Thats how it goes with characters who are more obscure, this happens with minor characters in X-men, but they can still grow in popularity. In the first X-men Kitty had a tiny cameo as a student who runs through a door by the end she's why Wolverine gets to travel back to the past in Days of Future Past.
Opportunities don't stay opportunities if they are squandered and Marvel needs to stop squandering Wanda. She's not going anywhere, all Marvel has to do is hire people to give her more priority. Marvel could switch her to the X-men any time they like, that's what they did to Bobby Da Costa and he's more obscure than she is. They made him team leader! Something being botched now isn't an excuse to give up. Opportunities come by trying, not by letting them go because of bad writing. The future is yet to be written, who knew something like Hickman's X-men would ever get published until it was published? What a character's "core" is doesn't come into it, this is about what the writers want and what editorial allows. And characters do change. Don't let the X-fandom get you down, they're not fans of Wanda and have no interest in understanding her. They don't get to decide Wanda's fate, Marvel does.
It sounds like you've given up.
Just because something is the status quo means it'll be the status quo forever. Who knew Bobby Da Costa would not only lead the Avengers but take over AIM? Thanks to Al Ewing that was a reality in 2015-2016. Maybe one day something like this will happen to Wanda.