“Not a puppet! Not a puppet! Not a puppet! Not a puppet!” The lyrics screamed by Chinese all-girl group Dummy Toys resonate their philosophy to a tee. Like Metallica’s “Master of Puppets,” the notion of being controlled by those in power pulling the strings has been a constant in heavy music. “We don’t want to be puppets of anyone or anything, and we don’t want to be restrained,” says guitaris...