In my experience, vocals tend to be considered a little less important than drums and guitars in metal. One of the most defining traits of early metal, indeed, was how it focused on riffs and solos (which in hard rock were always present, but weren't the core defining pieces of the composition). Of course, metal has invented entirely unique vocal styles, but otherwise it seems that metalheads generally consider the vocals as more the icing on the cake, and not part the cake itself. When I read reviews on this site, I generally notice that they almost always start with describing the guitars, drumming, and overall compositions before they get to vocals. Likewise, each genre has its sort of defined vocal style and bands don't put much of an emphasis on trying to be particularly unique in that regard. Like, there's just this very obviously "tech-death" style that a huge amount of tech-death vocalists use for...some reason. You can just hear it. Do you agree with this, or is this an uncharitable assumption? This is not to say that metal vocalists are untalented, far from it, mind you.