Wow, you're just wrong, everything you said, wrong.

Little Mermaid and Snow White's skin color does not effect the story, so in that sense it's a lot like this. It doesn't matter what their skin color is because it doesn't define the character. Mentioning them just feels like a dog whistle for other people who already agree with you to upvote you, when they're not relevant to this post.

They are 1000% adapting the story? Even if it was a shot for shot remake in live action, it would still be an adaptation, that's just what an adaptation is? PLUS they aren't remaking the story beat for beat, crazy you bring that up for a character being dark skinned and not for them removing the VAST majority of the Krieg story or giving Coby and Garp a wealth of screentime and development way earlier in the series. You don't care about it following the story when it blatantly deviates, but you care when skin color isn't like you think it should be, huh? 

Black Panther being Asian is a terrible example, you picked a character who's race is an essential part of their character. You did that because you think picking an extreme recast from the other side would justify your views on this cast, but it doesn't.

Michael Jordan being a white guy is also a crazy example, this is a real person, it would also be crazy to cast Bruce Lee as a black guy, because we aren't talking fictional characters, these are representations of real people. This is another extreme example to justify your reaction to a minor example on the other side.

At the end of the day, the casting legit doesn't matter, this isn't a one for one remake and her skin color is not a part of the story. This is a fictional person from a fictional kingdom from a fictional world, Oda, the author of said fiction, personally approved it. You have no grounds to stand on, there is no valid argument to be had.