Your rather strong opinion of To Kill a Mockingbird is.....a valid opinion as it belongs to you and hence cannot be 'wrong'....but it is quite different than that of many readers and teachers over the decades.
It has been and is still considered an American Classic....without the quotation marks. Often, it is called one of the greatest of American fiction. It is far and away not a 'feel good about yourself' novel or film. I've not seen the stage production yet. That's for February. Justice for blacks in the American south at that time was virtually non-existent. It would take a white "hero" to attempt to bring any sort of justice to a victimized black man...or woman....or child. The novel and the film calls attention to this racial injustice. Perhaps the characters could be considered too stereotyped.... i.e. these are the good guys...these are the bad guys.... but the novel and film starkly tells us to take a hard look at ourselves as a society.... America...the land of the free does not apply equally to all of her citizens.
Sadly, the subject matter today is relevant. The incarceration rate of minorities is racially motivated among other reasons. Perhaps the difference between then and now is justice is not necessarily based upon the lawyer being white....just as long as he/she is the best lawyer that money can buy.