How old was she in the comics when she became the Black Panther because she is sixteen in the movies? That is not believable no matter what happens in the comics, and people are not even into comics is why Black Panther made $700,000,000 in America. They never follow the comics to a tee, so that is really silly reasoning. You can scream about the comics all you want, but the iteration of her in the movies is not conducive to that whatsoever.
In the comics she’s young, maybe about 18-19 when she takes up the mantle.
The issue with Black Panther is that throughout the comic run there is only ever TWO black panthers. T’Challa and Shuri, and Shuri was only Black Panther for a relatively short time. The comics even had a huge war that retconned the continuity to allow T’Challa to take back the throne.
Also T’Challa has relatively few “sidekicks”, no mentees or apprentices. So there is no one that you can pluck from the canon comics that would make sense as Black Panther. He’s never even had any children that were within canon. So its not like a Batman situation where you have dikk Grayson, Tim Drake, and countless Batman scions.
So really the hard decision comes down to recasting or passing the mantle to Shuri. Now in the comics Shuri wasn’t much of an inventor/scientist, she was a warrior who was rather hot blooded and emotional. the Shuri from the movies is more like Q to T’Challa’s Bond, so there would have to be some broad leaps in character development to get her to that stage.
Which is why I feel like recasting at this point will be what Marvel ultimately does. Creating a brand new character that isn’t based off the lore of the canon would probably bring MORE backlash than recasting. Batman, Spiderman, hell even Blade have been recast and audiences understood.