Having actually met Terry Brooks, I can unequivocally tell you that the idea of him simply being a 'rubber stamp' for whatever the producers wanted to do is as about as far away from reality as it is possible to be.
Terry, like J.K. Rowling, made himself as available to the producers of The Shannara Chronicles as his schedule allowed, and was as hands-on as he possibly could be while also allowing them the creative freedom to do what they wanted.
You don't have to like the result, but trying to take a "purist" attitude doesn't do much other than make you come across as foolish and unbearably stubborn.
