Not defending Musk, but the point of humanoid robots is to perform a job currently done by a human worker without modifying the process or tools. Dedicated robot arms are fantastic for factory work, but the jobs they do have to specifically be designed to be done by a robot arm.

As an example, you can't put a robot arm at a human workspace and have it open a plastic bag, put an item inside it, and pick up a tape gun seal it with tape. For a robot arm to do that, the entire workspace, and extra robots would have to be added and programmed to accomplish the same task.