Ariel's race doesn't matter because she is Atlantean, a made up demographic. That said Blacks make up 13% of the US population and media directed at the American audience these days is overrepresenting them while mostly ignoring the soaring population of Hispanics.
To put this in perspective For every little black girl that is saying, "OMG she looks like me" there are like 9 non-blacks that are like, "Why did they change her mommy?"
We are living with the tyranny of the minority right now which is why gays, and trans characters are also vastly over-represented. Audiences are noticing this and are getting tired of it. I mean, how many times do you roll your eyes at the gay romance shoe-horned into every netflix show. Its just boring, and lazy, virtue signaling.
Again there is nothing wrong with Ariel being black, what is wrong is that all redheads are being replaced by black characters...lol.
Also, if you want to have more characters of color then make up some new ones...