The Wiz isn't even a remake of the Judy Garland movie. It's just another adaptation of the book by L. Frank Baum and is actually more faithful to the book than the original MGM movie. There are literally hundreds of versions of The Wizard of Oz all over the world. The 1939 MGM version just happens to be the most popular.
Besides, Baum never technically made references to characters' races. Dorothy could have easily been a black girl raised on a farm and since Oz is a fictional fantasy world, the characters could be any color. Also, since the book was published back in 1900, it's now in the public domain and has been for years, which means that anyone is free to make any version they like, which is why there are so many already.
White people have NO argument with this.