I disagree a little bit with you. Halle Berry's accent in X1 was pretty, pretty bad. I like Halle Berry as an actress in many movies but I don't think that she has a big range as an actress. She is a very limited actress and she could not elevate the little material she got. Yes, it is also problem of the script. But if you compare Halle Berry's Storm to Ellen Page or Evan Peters' X-Men work?! Both had minimal screen time but they still somehow manage to produce very interesting, compelling characters which feel like characters. This is what a great actor/actress does. I cannot see the same in Halle Berry's Storm and she had more screentime than Page and Peters. I don't know what technique Berry's uses in comparison to the other two but maybe she lacks a certain academic training? (just a careful guess. I don't know Berry's cv)...I love her dialogue scene with Nightcrawler in X2. But that's about it...
But in the end you are totally right, Singer as a white man is incapable to see a black character like Storm. He rotates around things he is capable to see: white (mainly male) characters!
If you were to re watch the X-Men trilogy and just focus on Storm's dialogue, her individual character arcs and on what she actually gets to do on screen. You might notice that Storm isn't written or directed to be a compelling character. Page and Peters though having limited screen timed did have decent dialogue and interesting things to do on screen. Sadly they same can't be said for Storm.
Most of her dialogue throughout the trilogy is exposition. She barely says anything meaningful or interesting. What's more she has very little interaction with other characters. It's almost like she has no relationship with any of the characters. We don't know who her friends are, whom she dislikes she treats everyone like a colleague despite the fact that she lives with these people.
I don't know how one elevates a character whose main purpose is to carry action and special effects sequences. You must credit Halle, she is very convincing when carrying those scenes and she shows commitment to her role by doing her own stunts. But beyond that the woman does not really get much to do.
She has so much screen time in X3 but watching that movie again, she doesn't really do much, she doesn't even have tha much dialogue.
Storm is badly written, directed, her character design and costume sucks. She doesn't really look or act like the Storm in the comics. You can't blame Halle for that.
Halle plays very well and believably this mousy, soft spoken, scared, weak ass black woman with white hair, because that's how her character is written. If the script says get your ass kicked by toad, then Halle has to get her ass kicked by toad.
Don't blame Halle. I'm confident if the character was written and handled by someone who knew and understood storm as a character, then Halle would nail the role. She has the talent, she just needs the material.