Spoilers for Spider-man: BND, which if you haven’t seen it yet, what are you doing, go see it.
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So I’ve been thinking about this for a while and here’s the thing about SM:BND.
Jean Grey in the source material is telekinetic before she’s telepathic. Yes, she’s telepathic EVENTUALLY, but she’s primarily telekinetic, at least at first, when she’s young.
And I can see why emphasizing the telekinesis angle with Sadie Sink would be perhaps a shade too close to Eleven from Stranger Things, and even just the telepathy is tricky if they make it too similar.
And thus, for this and other reasons I’m sure, they went with “she can hop into other people’s brains and possess them.”

Now, that IS a thing Jean Grey or any telepath can do. It’s a little strange to make it seem like that’s her primary power to start with.
She eventually levels up to psychic blasts that can freeze hundreds of people at a time, which is cool, and she is exhibiting telekinesis by the end of the movie (think of the floating glass shards), but it is still clear that possessing people is her main thing. She even uses that power to keep Peter’s body working after a certain key miscommunication with his extremely dangerous shooty friend.
But possessing people isn’t what Jean Grey is known for… but it is what KARMA is known for.

For those who aren’t quite as nerdy, Xuân Cao Mạnh is a Vietnamese mutant hero, who was a member of the New Mutants, eventually the X-Men, and other teams, created by Chris Claremont (yay!) and Frank Miller (ugh) in 1980. She may not be an original member of the team like Jean, but she’s an old school X-Men character. (She’s older than me!)
She’s also a lesbian. That’s not relevant just yet, but put in a pin in that.
And like I said, her power is telepathy-based and focused specifically on possessing other people. Basically exactly what Jean does in the movie.
So hang on… am I saying they stole Karma’s proper role and gave it to their young redhead it-girl they intend to build a franchise around? No, not necessarily, and I’m not saying that was the wrong thing to do.
Remember: Jean isn’t the only mind hopping telepath in this movie.
She’s on the warpath to find her sister Sara, who had the same power.
Now hang on. Did Sara exist in the comics and was she a telepath as well?
Sort of. She had some sort of mental resistance powers that helped her resist the Phoenix’s assault, and there was that whole kidnapping and mutation into an Atlantean (that’s a whole tangent), and Claremont apparently intended to have her develop a power to help other mutants unlock their own powers. But mostly she was a human ally of mutant kind, who then ended up kidnapped and murdered by anti-mutant terrorists. Which… well, you can see how you get to the movie version from those facts.
And I can see why they used her the way they did in the movie.
But if it had been up to me… I’d have used Karma instead of Sara Grey. Xuân would be the one who taught Jean to use her powers the way she does, because that’s how Xuân uses HER powers.
Everything unfolds exactly as it does in the movie, but instead of looking for her sister, Jean is looking for her ADOPTIVE sister. You see, they were both in foster homes, both kicked out of their families, both on the run. And they forged a strong friendship the way teen girl friendships are, with a little sapphic undertone. Maybe it’s unrequited, maybe Jean is a little bi-curious in the MCU, I don’t know.
But isn’t that a much more interesting and complex motivation for Jean? And also one that isn’t as clear cut for us, the audience? It challenges us to apply our empathy toward this character who has various dimensions of identity and oppression.
I just think that would have been super awesome.
Also, in my version of the story, there’s some sense that Karma isn’t actually dead. She moved her mind into someone else, or fractured it across various people. Not like that’s the first time it’s happened on screen for the X-Men.