If a class is "put on the bench", deemed "useless", that's a bad design decision. Besides, that acts as though the AST will do everything a WHM can (which it won't) and that they will be willing to. While the big heal numbers may not mean much, it allows WHMs to fix DPS mistakes when applicable.
AST probably is not going to be the best thing under the sun. Nor will it be the worst. We just have to wait for it, and then draw conclusions about it.